
Class G£U 

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COPYRIGHT DEPOSIT. 



ELEMENTS 



OF 



COMPARATIVE ZOOLOGY 



BY 



J. S. KINGSLEY, S.D. 

Professor of Zoology in Tufts College 



SECOND EDITION, REVISED 




NEW YORK 

HENRY HOLT AND COMPANY 
1904 



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Two Copies Recced 

NOV \ 1904 

Copyrignt - 

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Copyright, 1897, 1904, 



HENRY HOLT AND COMPANY 



ROBERT DRUMMONI), PRINTER, NEW YORK 



PREFACE TO THE SECOND EDITION. 

In preparing this edition many changes have been 
made; every page has been revised and some errors 
corrected. Several new illustrations have been added 
and directions for the study of other animals have been 
inserted. As in the first edition, greater prominence has 
been given to the vertebrate than to the non-vertebrate 
forms, since experience has shown that the work has been 
largely used as an introduction to or preparation for 
medical studies. The greatest change, however, has been 
in the separation of the laboratory work from the de- 
scriptive part of the text. Still, the pedagogica" advan- 
tages of the former arrangement have been maintained 
by numerous cross-references, while the systematic portion 
has a continuity which was lacking in the former edition. 

In the illustrations care has been taken to figure noth- 
ing which is studied in the laboratory. Students have 
been known to copy drawings rather than to work the 
details out from the specimen. 

Tufts College, Mass., June, 1904. 

iii 



PREFACE TO THE FIRST EDITION. 

The present volume is intended as an introduction to 
the serious study of zoology. It embraces directions for 
laboratory work upon a selected series of animal types and 
a general account of related forms. Laboratory guides 
are somewhat numerous, but general outlines of zoology 
adapted to beg'nners are few. By combining the two, 
it has been possible to emphasize the comparative side of 
the subject. A knowledge of isolated facts, no matter 
how extensive, is of little value in education, excepting 
as the powers of observation are trained in ascertaining 
those facts. Nature studies are truly educational only 
when the student is trained to correlate and classify facts. 
A considerable experience with students of different ages 
has resulted in the conviction that it is not sufficient to 
ask one to compare a grasshopper and a beetle, pointing 
out their resemblances and points of difference; leading 
questions must be asked. When the student has answered 
the questions under the headings "Comparisons' 7 in the 
following pages, he has a tolerably complete statement of 
the principal characters of the larger groups of the animal 
kingdom. 

Several considerations have had weight in the selection 
of types to be studied in detail. In the first place, so far 
as possible, these should be such as are readily obtainable 
in any. locality. But there are certain important groups, 
all the members of which are marine. The forms of these 

v 



vi PREFACE TO THE FIRST EDITION. 

which have been used can be purchased of dealers in 
laboratory supplies (see Introduction) at a cost of less 
than sixty cents per pupil. In the second place, the 
number of forms studied and the extent to which details 
of structure are worked out must be such that the work 
outlined can be done by students of average ability, in 
the time usually allotted to such work in the ordinary 
course. Especial care has been taken that time shall 
not be wasted in working out features of no morphological 
importance. Counting tail-feathers or fin-rays has no 
place in elementary zoology. 

Again, the work has been made largely macroscopic in 
character. Microscopes are expensive, and many institu- 
tions feel that they cannot afford to provide each student 
with one of these instruments. Then, too, there are 
enough important facts to be discovered with scalpel and 
hand-lens. Too many beginners have been lost among 
cell-theories and drowned in staining-fluids. These prop- 
erly come after the elements of the study have been 
mastered. 

In order of treatment the author has followed the se- 
quence which he believes productive of the best results- 
A strictly logical course would lead from the simple to the 
complex, but in practice this has not been found as valu- 
able as the order adopted here. 

A number of illustrations have been prepared especially 
for this work. Most of the others are credited to the 
author from which they are taken. It may interest some 
to know that Figures 39 and 123 were engraved for the 
second part of Agassiz and Gould's "Principles of Zool- 
ogy/' which was never published. 

Tufts College, Mass., June 14, 1897. 



CONTENTS. 



PAGE 

Introduction 1 

Equipment 2 

Material for Dissection 4 

Reference Books 10 

Laboratory Work. , 15 

Dogfish • 15 

Teleost 22 

Comparisons 30 

Frog , 32 

Tadpole 41 

Comparisons 43 

Turtle 44 

Snake 47 

Bird 48 

Comparisons 52 

Rat 53' 

Comparisons 64 

Crayfish or Lobster 67 

Sow-bug 73 

Comparisons. 75 

Grasshopper 76 

Comparisons 82 

Cricket 84 

June-bug 85 

Dragon-fly 86 

Bee or Wasp 87 

Comparisons 88 

Squash-bug 89 

vii 



mi CONTENTS. 

PAGE 

Butterfly , 90 

Comparisons 91 

Earthworm 92 

Comparisons 96 

Clam 98 

Oyster 102 

Squid 103 

Comparisons 108 

Starfish 110 

Sea-urchin 115 

Comparisons 118 

Sea-anemone 120 

Hydroid (Pennaria) 123 

Hydroid (Clava) 125 

Hydroid Medusa 127 

Comparisons 128 

Sponges 130 

Amoeba 132 

Paramecium 134 

Comparisons 136 



SYSTEMATIC ZOOLOGY. 

The Animal Kingdom 137 

Protozoa 145 

Rhizopoda 147 

Infusoria 149 

Sporozoa 151 

Summary 152 

Metazoa 154 

Summary 157 

Spongida 158 

Summary 161 

Ccelenterata 162 

Hydrozoa 165 

Scyphozoa 169 

Ctenophora 174 

Summary 176 



CONTENTS. ix 

PAGE 

Vermes 178 

Plathelminthes 178 

Nemathelminthes 182 

Annelida 183 

Molluscoidea 189 

Summary. „ , 190 

Mollusca 193 

Amphineura 197 

Gasteropoda 197 

Acephala 202 

Cephalopoda 208 

Summary 212 

Arthropoda 215 

Crustacea 218 

Acerata 231 

Merostomata 231 

Arachnida 232 

Insecta 235 

Chilopoda 235 

Hexapoda 236 

Summary. 270 

Echinoderma 273 

Asteroidea 276 

Ophiuroidea 278 

Crinoidea 279 

Echinoidea 280 

Holothuroidea 282 

Summary 284 

Chordata ' 286 

Tunicata 287 

Leptocardii 289 

Vertebrata 290 

Cyclostomes 315 

Pisces 317 

Amphibia 336 

Reptilia 342 

Aves 350 

Mammalia 363 

Summary 392 



CONTENTS. 



GENERAL ZOOLOGY. 

PAGE 

Comparative Physiology 395 

General Morphology 403 

Geographical Distribution 409 

Geological Distribution 413 

Evolution 414 

Index 421 



ELEMENTS OF COMPARATIVE ZOOLOGY. 



INTRODUCTION. 

Every true teacher must have his own methods , but 
some suggestions as to the way in which this book is 
intended to be used may be of value. In the first place, 
the laboratory work is regarded as most important, since 
through it the student is trained in observation — a train- 
ing utterly lacking in all the non-scientific studies of the 
school curriculum; and also since by it he acquires an 
autoptic knowledge of the animals studied. It is believed 
that every point mentioned in the laboratory directions 
can be made out by students in the high-school grades. 

In case the time be not sufficient to cover all the forms 
described, some may be omitted, but the writer thinks 
that any course should include at least the dogfish, teleost, 
frog, rat, crayfish, grasshopper, earthworm, clam, star- 
fish, sea-urchin, and sea-anemone. 

Each student should make all the drawings called for. 
Drawing the object seen is one of the greatest aids to 
observation, and every pupil, no matter how lacking in 
artistic ability, can make intelligible sketches of all points 
demanded. These sketches have great value for the 
teacher, since by their aid one can see at a glance any 



2 INTRODUCTION. 

errors or difficulties. All questions asked should be 
answered in the note-book. 

At various points are questions grouped under the head- 
ing ' Comparisons. ' These questions are based upon the 
previous laboratory work, and are intended to bring out 
clearly in the student's mind the essential points of resem- 
blance and of difference in the forms studied, and the 
bearings of the facts discovered. Laboratory work trains 
the powers of observation; the answering of such ques- 
tions leads to a systematization of knowledge and an 
exercise of the reasoning powers. The value of any 
scientific study lies not so much in the number or impor- 
tance of the facts learned as in seeing the relationships 
of these facts and the conclusions to be drawn from them. 
Hence each pupil should be required to hand in answers 
to these questions and to make the answers as detailed 
as possible. 

Following each list of comparisons is a reference to 
the pages where a general account of allied forms and 
a statement of the principal characteristics of the group 
may be found, thus giving a completeness to the knowl- 
edge which otherwise would be utterly lacking. In 
these general statements there are frequent references to 
the sections where the student has worked out the point 
for himself. In this way the work throughout will be 
based upon the inductive method, and finally the animal 
kingdom will be comprehended as a whole. 

Equipment. 

The room used for laboratory purposes should be well 
lighted and ventilated and should be furnished with 
running water. There should be receptacles, prefeiably 



INTRODUCTION. 6 

earthen jars, for waste, and the students should be made 
to keep everything clean. 

The tables for laboratory work should be low (not over 
29 inches from the floor), and should afford each student 
at least 6 square feet of surface. It is best that there 
should be no varnish upon them, as this makes trouble 
when alcohol is spilled. 

Each student should have the following instruments, etc. : 

Scalpel. Hand lens. 

Scissors. Jar of alcohol (or formol). 

Forceps. Note-book. 

Two dissecting-needles. Pencils (hard and soft). 

Dissecting-pan. Drawing-paper. 

As the animals to be dissected are small, the instruments 
should be of moderate size, delicacy being preferable to 
strength. The dissecting-pans (preferably of copper) 
should be about 6 by 12 inches, with flaring sides 1^ inches 
in height. The bottom should be covered to about 
i inch in depth with wax, so that the specimen may be 
pinned out during dissection. For most purposes it is 
better if the wax be blackened by lampblack. When 
possible the dissection should be carried on under water, 
as this tends to float up and separate the parts. At 
the close of each dissecting period the specimen should 
be placed in the jar of alcohol or formol for preservation 
until the next time. For this purpose the three-pound 
glass butter- jars with screw-tops are good. Battery- jars 
closed with a plate of glass may also be used. 

The pencils should be hard (6H, Faber), and the points 
should be kept sharp with a file or emery-paper. For 
drawings a smooth, hard-surfaced unruled paper is best, 
Bristol-board, aside from expense, being preferable. The 



4 INTRODUCTION. 

drawings should be in outline only ; shading should not 
be attempted. Frequently the use of colored pencils will 
make the sketches more intelligible, and for this purpose 
the following conventional colors may be suggested: 

Arterial circulation, red. Venous circulation, blue. 

Alimentary canal, brown. Liver, green. 

Kidneys, purple. Reproductive organs, yellow 
Nerves, gray. 

The laboratory should be provided with an oil-stone for 
sharpening instruments ; a pair of bone forceps * for cut- 
ting hard substances; a hypodermic and an injecting 
syringe for injection; a skeleton of at least one representa- 
tive of each great group of Vertebrates ; and at least one 
good compound microscope. It will also be advantageous 
to have a small equipment for microscopic mounting, 
as there are frequent opportunities for the preparation 
of objects of interest and value for demonstration to the 
class. 

Material for Dissection. 

The forms selected for study are, so far as possible, such 
as can readily be obtained in any locality by taking a little 
pains at the proper season. There are, however, certain 
groups of animals which occur only in the sea, and represent- 
atives of these must be obtained from the shore. These 
marine forms selected are Embryo Dogfish (Acanthias), 
Squid (Loligo), Sea-urchin (Strongylocentrotus, Arbacia), 
Starfish (Asterias), Sea-anemone (Metridium), Hydroid 
(Pennaria), and Calcareous Sponge (Grantia). The series 

* Side-cut pliers will do. 



INTRODUCTION. 5 

may be obtained from dealers* at a cost not exceeding 
sixty cents per student. Orders for these should be 
placed in the early summer, so that no difficulty or delay 
may occur later. Much of the other material may be 
obtained when wanted, but such as cannot be had in 
the colder months — frogs, tadpoles, snakes, turtles, 
crayfish, insects, earthworms, etc. — should be collected 
in the summer and preserved in alcohol or formol for 
use later. Those which require injection should be so 
prepared before being placed in the preservative fluid. 
Alcohol. — The most important of all reagents. It can 
be purchased, tax-free, by incorporated institutions of 
learning upon the fulfilment of certain conditions, which 
may be learned by application to the Collector of Internal 
Revenue in the district in which the institution is situated. 
As it comes from the distiller it is usually about 95% 
alcohol, the rest being water. This is too strong for 
most purposes, and for the preservation of material it 
should be reduced to 70% by the addition of water. 
A convenient method of making different strengths cf 
alcohol is as follows: First, with an alcoholometer, find 
the percentage of alcohol in the supply. Then fill a 
metric graduate with alcohol to the mark which corre- 
sponds to the desired per cent, and then add water until 
the mixture reaches the mark corresponding to the per 
cent, with which you started. Thus to make 70% from 
94% measure out 70 cc of alcohol, then add water until 

* Supply Department, Marine Biological Laboratory, Wood's 
Hole, Mass; Dr. F. D. Lambert, Tufts College, Massachusetts; 
H. H. and C. S. Brimley, Raleigh, N. C; Supply Department Hop- 
kins Laboratory, Stanford University, California. Skeletons and 
rarer forms can be obtained from H. A. Ward, Rochester, N. Y.; 
Kny-Shearer Co., 225 Fourth Avenue, New York. 



b INTRODUCTION. 

the mixture measures 94 cc. While not absolutely correct, 
the result is close enough for practical purposes. 

Formol. — This is a 40% solution of formaldehyde, and 
for use this should be reduced by addition of water to a 
2% or 3% solution {i.e., 1 part formol to 49 or 33 parts of 
water), in which specimens may be kept in good condition 
for some months. The same care must be exercised as 
with alcohol to change the fluid frequently while hardening 
the specimens. Formol has the disadvantage of evaporat- 
ing readily, and so the jars must be tightly sealed. It also 
has the disadvantage of freezing. 

A second substitute for alcohol is Wicker sheimer's fluid. 
This is made by dissolving 100 grams of alum, 25 of com- 
mon salt, 12 of saltpetre, 60 of potassic carbonate, and 20 
of white arsenic (arsenious acid) in 3 litres of boiling 
water. To this, when cold, add 1200 grams of glycerine 
and 300 of alcohol. Change the specimens once or twice, 
and keep them in at least twice their bulk of the fluid. 
This fluid has been highly recommended, but it is now 
little used, formol taking its place. 

Injections are made as a means of more readily following 
tubular structures, especially blood-vessels, and consist in 
forcing into these tubes colored material which will render 
them more easily recognized. For many injections simple 
apparatus may be used. Thus frequently a glass tube 
drawn out to a point can be filled with the injecting fluid 
and then, when the end of the tube is inserted into the 
blood-vessel, the fluid can be forced into the artery or vein 
by the pressure of the breath or by a large rubber bulb. 
It is, however, more satisfactory to use the regular inject- 
ing syringe, sold by all dealers in naturalists' supplies. 
These are provided with small tubes (canulas) for insertion 
into the vessel to be injected, and these are grooved at 



INTRODUCTION. 7 

the tip so that they may be firmly tied into the artery or 
vein. 

Most of the injections called for in the present work 
can be made either through the aorta or through the ven- 
tricle. The ventricle is cut open and the canula is forced 
through this opening into the aorta, around which a string 
is passed and tied, thus holding the tube firmly in place. 
The syringe is then filled with the injecting fluid (see 
below) and connected with the canula, when a pressure 
upon the piston will force the fluid into the blood-vessels. 
Too much pressure should not be exerted, as the vessels are 
liable to rupture. It is advantageous in many cases to 
first inject with 2% formol, which washes out the vessels 
and helps to preserve the specimen. Then the colored 
mass is employed. 

Various injecting fluids have been proposed, but the 
following are ample for all purposes, and they have, be- 
sides, the advantage of not requiring heat, which in the 
case of some forms causes a softening of the walls of the 
blood-vessels. 

Starch Injection Mass. — Grind together in a mortar one 
volume of dry starch, one of a 2J% aqueous solution of 
chloral hydrate, and one-fourth volume each of 95% alcohol 
and of the ' color.' The ' color' consists of equal volumes 
of dry color (vermilion, chrome yellow, Prussian blue, etc.), 
glycerine and alcohol. The mixture will keep indefinitely, 
but requires thorough stirring before use and quick usage, 
as the starch and color settle rapidly. 

Gum Injection Fluid. — Make a rather thick (molasses- 
like) solution of gum arabic in water ; color it with carmine 
dissolved in ammonia or with soluble Prussian blue, and 
strain through muslin. With the addition of a little thymol 
the fluid will keep well if tightly corked. After in- 



8 INTRODUCTION. 

jection place the animal in alcohol, which hardens the 
gum. 

By using both injection masses in succession the complete 
circulatory system may be injected (double injection). To 
accomplish this, first inject with the gum fluid, colored blue, 
and then follow with the starch mass colored red. The 
gum will flow through the finest vessels, but the starch 
mass will stop at the capillaries. 

Study of Vertebrate Brains. — If material be abundant 
the study of the brain and its nerves will be much facili- 
tated by putting heads of the various forms in the fluid 
mentioned below a week or two before the dissection is to 
take place. The fluid, which should be changed two or 
three times, softens (decalcifies) the bones, and at the 
same time hardens the nervous structures. It is composed 
of equal parts of 95% (commercial) alcohol and 10% nitric 
acid. The heads should be washed for an hour or two 
in water before dissection, as otherwise the acid will attack 
the dissecting instruments. 

Muller's Fluid is also used for the preservation of 
brains and nervous matter, but it does not decalcify. In 
its use the cavity of the skull should be opened so as to 
permit free entrance of the fluid. It should be changed 
in twelve hours, one day, one week, and four weeks. 
It colors all tissues a dirty green. Muller's Fluid is com- 
posed of 

Sulphate of soda 1 part 

Bichromate of potash 2 parts 

Water 100 " 

Fuchsin is one of the most easily used stains. It is made 
by dissolving 1 part of the aniline dye in 200 parts of 
water. 



INTRODUCTION. 9 

Alum Cochineal is made by soaking 7 parts of crushed 
cochineal insects and 7 parts of alum in 700 of water for 
twenty-four hours. Then boil until the amount is reduced 
to 400 parts. Allow to stand twenty-four hours, filter, 
and add a little thymol to keep it from spoiling. This 
stain has the advantage of not overstaining specimens. 
Objects may be left in it from twelve to twenty-four hours. 

Grenadier's Borax Carmine. — Two grams of carmine 
are dissolved in a solution of 4 grams of borax in 100 cc 
of water. Then 100 cc of 70% alcohol are added, the 
whole allowed to stand twenty-four hours, then filtered. 
A convenient method of use is to add about 1 part of 
the stain to 25 of acid alcohol (100 cc of 70% alcohol 
plus 5 drops of hydrochloric acid). After staining, place 
the specimen for a few minutes in 70% alcohol to which 
a little ammonia has been added. 

Picrosulphuric Acid is used for killing many animals 
without distortion. It is made by dissolving picric acid in 
water until no more will be taken up, and then adding to 
100 parts of the solution 2 parts of sulphuric acid. It 
is allowed to stand a day, is filtered, and is prepared for 
use by adding 3 parts of water to 1 of the stock solution. 
Specimens killed in this fluid are stained yellow, and 
should be washed in several changes of water before 
being placed in alcohol or formol. It takes from one to 
three hours to kill. 

Further directions for the preservation of material and 
for microscopic study and preparation may be found in 
the various histologies (Stohr, Bohm and Davidoff, etc.) 
and in Lee's " Micro tomist's Vade Mecum" (Philadel- 
phia). Recent methods and improvements are described 
in the Journal of Applied Microscopy (Rochester) and the 
Journal of the Royal Microscopical Society (London). 



10 introduction: 

Reference Books. 

In the classroom there should be some works of reference 
and the teacher should have and use others. As an aid in 
selection of these works the following remarks may be of 
value : 

There are a number of guides for the dissection of ani- 
mals. One of the oldest and best of these is the " Practical 
Biology" of Huxley and Martin (Macmillan & Co.), which 
deals with both plants and animals in a thorough manner, 
although but a few forms are included. Of a somewhat 
similar character is Dodge's "Elementary Practical Biol- 
ogy " (Harper & Brothers), which enters more into the 
physiological side of the forms studied. The "Practical 
Zoology" of Marshall and Hurst (Putnam) is confined 
solely to animals, which it describes in a thorough manner. 
Descriptions of more forms of Invertebrates will be found 
in Bumpus' "Invertebrate Zoology" (Holt), Pratt's 
"Invertebrate Zoology" (Ginn), and Brooks 7 "Inverte- 
brate Zoology" (Cassino), the latter treating of the em- 
bryology of some as well. For Vertebrates there are 
Parker's "Zootomy" (Macmillan), and anatomies of the 
cat by Gorham and Tower (Putnam), Reighard and 
Jennings (Holt) and Davison. 

For general accounts of the structure of animals, giving 
general statements for all groups, Jackson's edition of 
Rolleston's "Forms of Animal Life" (Macmillan) and 
Gegenbaur's " Comparative Anatomy " (out of print; only 
to be found second-hand) are good. The general struc- 
ture of invertebrate forms is covered by Lang's 'Text- 
book of Comparative Anatomy" (Macmillan), Shipley's 
"Invertebrate Zoology" (Macmillan), McMurrich's "In- 
vertebrate Morphology" (Holt), and Huxley's "Anatomy 



INTRODUCTION. 11 

of the Invertebrates" (Appleton). Of these Lang's work 
is the most detailed; Huxley's is rather old; Shipley's is 
the simplest. The structure of the vertebrates will be 
found in Wiedersheim's " Comparative Anatomy of the 
Vertebrates" (Macmiilan), Huxley's " Anatomy of the 
Vertebrates" (Appleton), and Kingsley's " Vertebrate 
Zoology" (Holt). 

The development of animals is discussed in the following 
works: Balfour's " Treatise on Comparative Embryology" 
(Macmillan) , Korschelt and Heider's " Text-book of Em- 
bryology" (Macmillan), Hertwig's "Text-book of Em- 
bryology "(Macmillan), and Minot's "Human Embryology" 
(Wm. Wood & Co.). Balfour's treatise is a standard, but 
is rather old. Korschelt and Heider deal only with in- 
vertebrates; Hertwig and Minot only with vertebrates. 
McMurrich's "Development of the Human Body" (Blak- 
iston) is a smaller work treating almost entirely of the 
development of mammals. 

Within a few years several good general zoologies have 
been published. Under this head are included works 
which treat of the structure, development, classification, 
etc., of animals. Prominent among these are the "Text- 
book of Zoology" by Parker and Haswell (Macmillan) 
and Kingsley's translation of Hertwig's "Zoology" (Holt). 
Larger works are the "Cambridge Natural History" and 
a "Treatise on Zoology" (Macmillan), now in course of 
publication. The "Riverside Natural History" (Hough- 
ton, Mifflin & Co.) and the "Royal Natural History" are 
more popular in character. Among the more elementary 
works may be mentioned the zoologies of Jordan and 
Kellogg, Colton, Weysse, and Davenport. 

The broader and more general biological principles, 
without reference to classification and description of forms, 



12 INTRODUCTION. 

maybe found in Parker's " Elementary Biology" (Macmil- 
lan) and Hertwig's " General Principles of Zoology" (Holt). 

Besides these there are a number of good works treating 
of special groups of animals. The student at the seashore 
of our New England States finds Verrill and Smith's " In- 
vertebrates of Vineyard Sound" indispensable. This was 
published in the Report of the U. S. Fish Commission for 
1871-2, but separate copies may be had from dealers in 
scientific books. A broader range of forms and wider 
geographical limits characterizes Arnold's "Sea Beach at 
Ebb Tide" (Century Co.). Emerton's "Life on the Sea- 
shore" (Cassino) covers much the same ground, but in a 
more elementary manner. For the identification of 
vertebrates Jordan's "Manual of the Vertebrates" (Mc- 
Clurg) is the standard. There are two good works upon 
molluscs, Woodward's "Manual of the Mollusca" (London) 
and Tryon's "Structural and Systematic Conchology," 
3 vols. (Philadelphia), both well illustrated. The insects 
are well treated in Comstock's "Manual of the Study of 
Insects" (Comstock Pub. Co., Ithaca, N. Y.), Howard's 
"Insect Book" (Doubleday, Page & Co.), and Hyatt and 
Arms' "Insecta" (Heath, Boston). An older work, but 
still of great value, is Harris' "Insects Injurious to Vege- 
tation" (Boston). The butterflies and moths are well 
illustrated and described in Holland's " Butterfly Book" 
and "Moth Book" (Doubleday, Page & Co.). 

There are several works dealing with birds. Of these 
possibly Chapman's "Birds of North-Eastern America" 
(Appleton) and Coues' "Key to North American Birds" 
(Estes & Lauriat) are most widely known. Ridgeway's 
"Manual of North American Birds" (Lippincott) is also 
good, as is Chamberlain's edition of Nuttall's "Ornithol- 
ogy" (Boston). 



INTRODUCTION. 13 

There are also several more special works which are of 
great value in the laboratory or study-room. Among 
these are Huxley's " Crayfish " (Appleton & Co.), Ecker's 
" Anatomy of the Frog" (Macmillan), Darwin's " Earth- 
worms and Vegetable Mould" (Appleton) and his "Coral 
Reefs." Dana's "Corals and Coral Islands" (Dodd, Mead 
& Co.) is a later work. Flower and Lydekker's "Mam- 
malia" (Edinburgh) is excellent. The teacher will find 
much valuable material in the zoological articles in the 
Encyclopedia Britannica, though these are very unequal 
in treatment. Some of the best of them have been re- 
printed in "Zoological Articles" by Lankester and others 
(A. & C. Black). 

A dictionary of scientific terms is frequently asked for. 
Any of the more recent unabridged English dictionaries 
will contain almost every zoological term one runs across. 
Several so-called dictionaries of scientific terms have been 
published, but as yet not one of any value has appeared. 

The teacher should remember that science is continually 
growing, and that text-books and manuals grow old. He 
should therefore have access to some of the scientific jour- 
nals. Among those most valuable to the teacher of natu- 
ral history are the American Naturalist (Boston) and 
Biological Bulletin (Lancaster, Pa.). Nature (London) 
and Science (New York) are weekly publications which 
include all sciences. The Journal of the Royal Micro- 
scopical Society (London) is valuable, since it contains not 
only an account of new methods, but summaries of recent 
investigations in both botany and zoology. Its price is 
unreasonably high. 



PAET I. 
DIRECTIONS FOR LABORATORY WORK. 

EMBRYO DOGFISH (Acanthias). 

Material. — For each student a specimen of the late embryo 
of Acanthias, known to the fishermen as ' dog-fish pups. ' This 
should have at least the arterial system injected (easiest done 
by partly cutting off tail behind last dorsal fin and injecting 
the caudal artery). 

One or more slides of the skin of the ' pup. ' These may 
be prepared an hour or more before the laboratory period 
by placing a bit of the skin on a microscopic slide in a drop 
of glycerine and covering it with a bit of cover-glass. Such 
preparations are but temporary; permanent mounts which 
can be used year after year may be made as follows : The piece 
of skin, I inch square, is placed for 30 minutes in each 95% and 
absolute alcohols and then in spirits of turpentine. It is then 
placed for a moment on a bit of filter-paper to remove the 
superfluous turpentine, placed in a drop of balsam on the 
slide and the cover-glass applied. Another slide of the decal- 
cified skin stained and cut in sections will show other features 
of the scales. 

General Topography. Distinguish in the fish anterior 
and posterior, right and left, back (dorsum) and belly 
(venter). Is the animal bilaterally symmetrical? i.e., 
are the right and left sides alike? Do you recall any 

15 



16 LABORATORY WORK. 

animal without bilateral symmetry? Make out the re- 
gions, head, trunk, and tail. Is there a neck? Where is 
the vent? 

How many fins do you find? How many are paired 
and how many unpaired? Are any in the median line 
of the body? Can the fins be regarded as folds of the 
skin? The various fins have names. The median fins 
are the dorsal on the back, the anal on the ventral surface 
just behind the vent, and the caudal at the end of the tail. 
Do you find a skeleton in any of these? Is the caudal fin 
homocercal (with equal lobes) or heterocercal (with unequal 
lobes) ? The paired fins are, in front, the pectorals; behind, 
the ventrals. Do these compare, in position, with your 
own limbs? 

How many eyes are there, and where are they placed? 
Are they movable? Are eyelids present? Notice in 
each eye the colored iris around the black pupil* 

How many nostrils and where are they? Examine 
carefully and see how the opening is subdivided by a 
flap of skin. Sketch. Probe with a bristle and see if 
the nostrils connect with the mouth or throat. How 
does this compare with what occurs in yourself? 

Where is the mouth? Is there a tongue? Do you 
find any ears? Behind the eyes are a pair of openings, 
the spiracles; probe and see if they communicate with 
the throat. On the sides of the neck, in front of the 
pectoral fins, are the gill-slits or branchial clefts. How many 
are there? 

Draw the fish from the side, natural size, inserting and 
naming all the parts made out. 

* In preserved 'pups' the lens may be whitened so that the 
pupil appears white instead of black. Colors also fade in alcohol or 
formol, 



DOGFISH. 17 

In the prepared slide of the skin ; under a low power 
of the microscope, see the scales, drawing several of them 
in thier relative positions. Each scale consists of a basal 
plate bearing an oblique spine (dermal tooth). This type 
of scale is called placoid. Do the scales overlap? 

Internal Structure. 

Open the fish by cutting in the mid-ventral line from 
the vent forward to just behind the pectoral fins, and 
then make cross-cuts at either end so that the siclewalls 
of the body may be pinned out in the dissecting-pan. 
Fill the pan with water so that all parts are covered. 

This lays open the body cavity, or ccelom ; notice that it is 
everywhere lined with a smooth membrane, the peritoneum. 
Through this membrane see that the muscles of the body- 
wall are arranged in plates (myotomes) extending from 
dorsal to ventral surface. 

Trace the alimentary canal. In the front part of 
the body-cavity is the liver with two large lobes and 
dorsal to it the J -shaped stomach. The intestine begins 
at the end of the J and extends back to the vent. In 
the intestine recognize a large anterior portion and a 
smaller posterior rectum, with a blind sac, the rectal 
gland, near the junction of the two. Cut a bit of the 
wall from the larger part of the intestine with the scissors 
and notice the spiral valve in its interior. What function 
can you suggest for it? 

At the bend of the stomach is the triangular spleen; 
at the junction of stomach and intestine is the pancreas. 
Do you find any thin membranes (mesenteries) binding the 
alimentary tract to the dorsal wall of the coelom? Or 
any similar membrane es (omenta) connecting the various 



18 LABORATORY WORK. 

parts of the tract together? Notice blood-vessels passing 
from the mid-dorsal line of the ccelom (dorsal aorta) to 
the intestine (anterior mesenteric artery), to the rectal 
gland (posterior mesenteric artery), and one more anterior 
(ccelice axis) to stomach, liver, and anterior part of intestine. 

Draw the alimentary tract as made out, inserting and 
naming all parts. 

Remove the alimentary canal by cutting away most 
of the liver, the stomach, and the rectum. On the roof 
of the ccelom are two long ridges either side of the mes- 
entery. The lateral ones are the ' kidneys,' or Wolffian 
bodies (mesonephros) , the much shorter medial ones are 
the reproductive organs (gonads). Draw this system. 

Cut off the skin between the pectoral fins and clean the 
muscles from the support of the fins (pectoral girdle) 
which crosses the median line. Is this composed of bone? 

Cut through the pectoral girdle and lay open the cavity 
in front of it (pericardial cavity). In this lies the heart, 
consisting of a thick-walled ventricle below, and dorsal 
to it a thinner-walled auricle. The heart is connected to 
the posterior wall of the pericardium by a thin-walled 
sinus venosus. In front of the heart and extending for- 
ward to the anterior wall of the pericardium is a large 
blood-vessel, the truncus arteriosus. Sketch the heart, 
pericardium, etc. (ventral view), and then trace the 
truncus forward into the flesh in front of the pericardium, 
cutting carefully. This part is the ventral aorta. Trace 
from it, right and left, afferent branchial arteries carrying 
the blood into the partitions between the gill-clefts. 
Add these vessels and the clefts to the sketch of the heart. 

Insert the scissors at the angle of the jaws and cut back- 
wards along the lower edge of the gill-slits; repeat the 
operation on the other side and turn back the lower jaw 



DOGFISH. 19 

and floor of the throat as a flap. This will lay open the 
cavity of the mouth and the pharynx. 

See that the gill-clefts are slits in the wall of the tube, 
each slit bearing delicate filaments on its walls, while a 
bar of cartilage {branchial arch) lies in each partition 
between two successive gill-clefts. See also the internal 
opening of the spiracle. Is there a bar of cartilage (hyoid 
arch) between it and the first gill-cleft? Could the spiracle 
be regarded as a modified gill-cleft? Draw these parts X4. 

Slit the skin on the roof of the mouth and carefully 
remove it with the forceps. This will expose the efferent 
branchial arteries, which can readily be traced from the 
septa between the gills to their union to form the dorsal 
aorta, which runs backward above the alimentary canal. 
Taking the two aortse and the branchial arteries into 
consideration, could you consider the circulatory system 
as consisting of two tubes, one on either side of the alimen- 
tary canal, connected by pairs of semi-circular vessels? 
Draw a diagram illustrating the relations of the blood- 
vessels to the alimentary canal and the gill-slits. From 
the anterior efferent branchial trace the common carotid 
arteries of either side forward and toward the middle 
line to their union where the internal carotid is given off, 
noting the external carotid about half way between the 
branchials and the internal carotid. Add these arteries 
to the sketch of the roof of the mouth and gill region. 

Cut off the tail with a sharp scalpel just in front of the 
posterior dorsal fin and in the cut surface make out the 
following points: In the centre a gelatinous rod, the 
notochord, with a tough notochordal sheath around it. 
Dorsal to the notochord is the spinal cord (nervous), while 
below it are two blood-vessels, the caudal artery and vein. 
Extending from the notochordal sheath, around these 



20 LABORATORY WORK. 

structures are two arches of cartilage, a neural arch around 
the spinal cord, a hcemal arch around the blood-vessels. 
The bulk of the section is occupied by the muscles of the 
tail. Note that the two halves are separate and that each 
half is subdivided into dorsal and ventral muscles. On 
either side of the body, just beneath the skin, is a minute 
tube, the canal of the lateral-line system. Sketch the cut 
surface of the tail, illustrating all these points. 

Split the skin on the top of the head and pull it 
off, noticing on its under surface other branching canals 
of the lateral-line system. 

In the head of the pup it will be difficult to make out 
much of the brain and nerves, but the following points 
can be seen and followed with ease. 

Carefully slice off the top of the skull, exposing the brain. 
Enlarge the opening until the whole brain is visible and 
then make out the following parts: In front the cere- 
brum, made up of right and left halves, each prolonged 
at the lateral anterior angle into an olfactory tract leading 
toward the nostril. Behind the cerebrum and lying at 
a lower level is the 'twixt-brain (optic thalamus), which has 
a thin roof. Next come the optic lobes, & pair of rounded 
prominences meeting closely in the middle line. The optic 
lobes are overlapped behind by the unpaired cerebellum, 
which extends backwards and similarly overlaps the fifth 
region of the brain, the medulla oblongata, portions of 
which, the corpora restiformia, are visible at the sides of 
the cerebellum. Draw the brain in outline, naming the 
parts. 

The principal nerves you will find will be the olfactory, 
already mentioned, going to the nose; the optic, arising 
from the lower surface of the 'twixt-brain and going to 
the eyes; the trigeminal, arising from the anterior side 



DOGFISH. 21 

of the medulla, just below the corpus restiforme and pass- 
ing forward to supply the 'face.' Just behind this are 
the combined facial and auditory nerves which supply the 
face and ear. Still farther back is the large vagus arising 
from the side of the medulla and going to the gills, the 
lateral line of the trunk, and the heart and stomach. 
Trace these nerves as far as possible and add them to the 
sketch of the brain. 

Cut off the snout by an incision passing through the 
nostrils, and in the cut surface see the folds of the olfactory 
membrane. What reason can you suggest for the folding? 
Sketch the cut surface. 

Have you found bone in any part of the dogfish? 



TELEOST— BONY-FISH. 

Material. — For each student a specimen of any common 
fish — perch, sucker, pout, cunner, etc.- — from eight to twelve 
inches in length. Great care should be taken that the material 
is obtained in a perfectly fresh condition, as the viscera decay 
rapidly. The body-cavity should be opened so as to permit 
free access of the preservative fluid (formol, alcohol) and the 
alimentary canal should be injected with it through the vent. 
The arterial system should be injected with starch mass or 
gum mass (see introduction) through the ventricle of the heart 
and through the caudal artery. 

For the study of the brain the head of a second fish (cod's 
heads from the market are good) should be placed in a large 
quantity of nitric alcohol (see introduction) about a week 
before the laboratory exercise. It should be rinsed in run- 
ning water for two hours before dissection to remove the acid 
from the tissues. This decalcifying fluid will so soften the 
bones that they may be cut readily with the knife, while the 
nervous structures are preserved in good condition. 

The laboratory should a'so have a prepared skull of some 
fish like a cod or perch, as well as a number of vertebrae from 
the table. 

Topography of Body. Distinguish in the fish, anterior 
and posterior, a back (dorsum) and a belly (venter), and 
right and left sides. Make out the regions: head, trunk, 
and tail. Is there a neck? Where is the mouth? the 

vent? 

22 



BONY-FISH. 23 

How many fins can you find? How many are in pairs? 
How many single? Are any in the median line of the 
body? Is there a skeleton to the fins? Could you regard 
a fin as a fold of the skin supported on soft or spiny rays? 

Of the median fins the caudal terminates the tail, the 
dorsal is on the back, the anal is just behind the vent. 
Are there two of any of these? Are the upper and lower 
lobes of the caudal equal (homocercal) or unequal (hetero- 
cercal) ? 

Can the paired fins be compared in position to your 
own. limbs? By feeling, ascertain if there be any solid 
support in the body for either pair. How does this con- 
dition compare with that in man? The anterior paired 
fins are the pectorals; the posterior are the pelvic or ven- 
tral fins. 

Integument. On the trunk and tail are scales. Are 
they regularly arranged? Are there scales on the head? 
Do they extend on the fins? Is there any skin over the 
scales? Is there skin on the head? Can you trace the 
skin of the head into the mouth? Find dark pigment 
spots on the body. Does the color belong to the scale or 
to what? Settle by pulling out a scale. 

Notice the lateral line running along a row of scales on 
either side of the body. Does it continue on the head? 
Examine the scales with a hand-lens and see what causes 
the line. Examine any scale with the hand-lens. Is its 
margin regularly rounded (cycloid), or is it toothed or 
spiny behind (ctenoid)? 

The Head. How many eyes are there? Where are 
they placed? Are they movable? Are eyelids present? 
Notice in each eye the colored iris around the central 
black pupil* 

* Here as elsewhere in these directions color is given as in the 
fresh fish. In preservative fluids colors change and fade. 



24 LABORATORY WORK. 

What is the position of the mouth? See that it has 
a bony framework, the upper jaw being composed of a 
premaxillary in front, and behind this a maxillary which 
when the mouth is open slides over the dentary or lower 
jaw. Do any of these bones bear teeth? Open the mouth 
and examine the tongue. How much can it move? Can 
you find teeth anywhere inside of the mouth? Feel with 
a pin. 

How many nostrils, and where situated? Probe with a 
bristle. Do they communicate with the mouth? Can you 
find any ears? 

The Branchial Apparatus. Find the gill-opening, a 
crescentic slit on the side bounding the head behind. In 
front of it is the gill-cover or operculum, which may be 
divided into the operculum proper (composed of several 
parts) and the branchiostegal membrane, supported by the 
bony branchiostegal rays, which completes the apparatus 
below. Connecting the branchiostegal region with the 
trunk is the narrow isthmus, separating the gill-openings 
of the two sides. 

Lift the operculum and see the gills. Each is composed 
of rows of red gill-filaments supported on a branchial arch. 
Between the successive arches are the gill-clefts. How 
many are there of these? Open the mouth and see how 
the gill-clefts are connected with the posterior part 
(pharynx) of the cavity. Could you regard them as slits in 
the wall of a tube? Notice that each arch contains a 
solid support. Can you see a red blood-vessel running 
along each arch? 

Draw a sketch of the left side of the body, inserting and 
naming all parts that can be seen from the surface. 



BONY-FISH. 25 

Internal Structure. 

With scalpel and forceps remove a piece of skin from one 
side of the fish, exposing the underlying muscles. Notice 
that these are arranged in chevron-like plates, each plate 
(myotome) extending from back to belly, and being divided 
into dorsal and ventral portions. Pick among the ventral 
parts of the muscle-plates. Do you find any ribs? How 
are they arranged with regard to the myotomes? 

Open the fish by cutting with the scissors from just in 
front of the vent, forward, in the median line, to the 
pectoral fins, taking care to cut nothing but the body-wall. 
Make other incisions transverse to the first, so that the 
body-wall on either side may be turned out like a flap, 
thus opening up the body-cavity, or coelom, containing the 
viscera. Without further dissection notice the membrane 
(peritoneum) lining the cavity. Is it silvery or pigmented? 
In the front part of the cavity is the large reddish or 
brownish liver; turn this over to the left and expose the 
stomach, connected apparently with the front wall of the 
body-cavity. Pass a probe from the mouth through the 
oesophagus or gullet into the stomach. From the stomach 
the intestine passes back to the vent. From what part of 
the stomach does it arise? Is it straight? How is it 
supported in its position? 

In many fishes worm-like blind tubes (pyloric co3ca) 
arise at the junction of stomach and intestine. Their 
purpose is to increase the surface secreting the digestive 
fluids. Do any of these occur in your fish? 

Study the liver more carefully. On its anterior surface 
see blood-vessels (hepatic veins). Where do they go? On 
its posterior surface is the thin-walled green or yellow gall- 
bladder. Can you trace any connection between liver and 
intestine? 



26 LABORATORY WORK. 

Where is the thin membrane (mesentery) supporting the 
intestine attached to the body-wall? Can you find blood- 
vessels in it? From where do they seem to come? 

Pull the intestine to one side, and expose the reproduc- 
tive organs in the posterior part of the body-cavity. In 
the male the testes are usually white; in the female the 
ovaries yellow or pink. Both vary in size according to 
the season. Are these structures paired? Trace their ducts 
backwards, and see where they empty. In the dorsal 
part of the body-cavity look for the air-bladder (lacking 
in some fishes). Can you find a duct connecting it with 
the oesophagus? 

Make a drawing from the side showing the organs 
studied, and leaving space for additions. Then cut away 
these parts and find, dorsal to the air-bladder, the long, 
dark red kidneys. Are they enlarged in front (head- 
kidneys) V Can you trace the kidney duct? 

Continue the median ventral incision forward between 
the pectoral fins nearly to the isthmus, taking care as 
before not to cut the underlying parts. Cut away the 
thin partition (false diaphragm) just in front of the liver„ 
This will lay open the pericardial cavity (part of the 
ccelom) . 

In the pericardial cavity lies the heart. It consists of 
a triangular ventricle below (in the normal position of the 
fish) and a more dorsal auricle. In front the ventricle 
gives off a blood-vessel, which at first has a conical enlarge- 
ment (arterial bulb), and then is continued forward as the 
ventral aorta. Eehind the heart is a blood-cavity (venous 
sinus) extending across the body-cavity in front of the 
false diaphragm. How are the hepatic veins (p. 25) 
related to this? 

Follow the ventral aorto forward through the muscu- 



BONY-FISH. 27 

lar tissue, tracing its branches {afferent branchial arteries) 
into the gill-arches (p. 24). What relations do these 
branchial arteries and ventral aorta bear to the pharynx? 

Now cut away the floor of the throat and trace in the 
gill-arches the efferent branchial arteries to their union 
above the gullet in the longitudinal blood-vessel, the dorsal 
aorta. Can you find this aorta in the roof of the peritoneal 
cavity? Could the blood-system, so far as you have studied 
it, be described as two longitudinal vessels lying on either 
side of the alimentary canal, and connected by a series of 
paired transverse vessels? What must be the course of 
the blood in the different parts of the system? Draw a 
diagram illustrating the relations of the circulatory appa- 
ratus to the alimentary canal and gill-slits. 

Pick into the side of the tail until the back-bone {vertebral 
column) is reached. Take out a small piece of it and clean 
it by boiling a few minutes in a beaker or test-tube.* 
Wash away the flesh, and see that it is made up of a series 
of bones {vertebrae), arranged one after the other. Exam- 
ine a single vertebra, making out the following parts: 
(1) A body or centrum, shaped like an hour-glass and 
hollow at either end {amphicoelous) . Do the hollows of 
the two ends connect? (2) Arising from the centrum 
two bony plates {neural processes), uniting above into a 
single neural spine. These together form a neural arch; 
so called, since the great nervous {neuron, nerve) struc- 
ture, the spinal cord, passes through it. (3) On the oppo- 
site or ventral side of the centrum a similar hcemal arch, 
composed of hcemal processes and h&mal spine, so called 
because the caudal blood-vessels pass through the arch 
{haima, blood). 

* A few vertebrae from the table will answer equally as well. 



28 LABORATORY WORK. 

Examine in the same way a vertebra in the trunk 
region. Can you find the same parts? Do the ribs 
correspond to neural processes or to haemal processes, 
or are they something different from either? 

Draw a front view of trunk and caudal vertebrae, naming 
the parts. 

In another bit of the back-bone, near the head, see 
the spinal cord passing through the neural arch. Can 
you find any nerves given off from it? How are they 
arranged? 

In the tail region see blood-vessels passing in a similar 
manner through the haemal arch (haima, blood). Pull 
apart two vertebrae and see what fills the cavities in the 
ends. 

Cut off the head,* and after picking away the muscles 
at the hinder part of the skull above, carefully slice off 
the top of the skull with a strong knife, taking only thin 
slices and exercising great care after the cavity of the 
skull is exposed. Enlarge the opening by picking, and 
then with great care pull away the loose gray matter 
which covers the white or pinkish brain. When this is 
exposed make out in it the following parts, beginning in 
front : 

(1) The olfactory lobes tapering in front into the nerves 
going to the nostrils (p. 24). 

(2) Two rounded oval masses (cerebral hemispheres) 
meeting in the middle line in front, and together constitut- 
ing the cerebrum. 

(3) The Hwixt-brain, also two-lobed, but lying at a 
lower level. 

(4) The large, paired, rounded optic lobes. 

* These steps are best taken with the decalcified skull (p. 22). 



BONY-FISH. 29 

(5) The unpaired cerebellum crowded in between the 
optic lobes behind and extending back over the base of — 

(6) the medulla oblongata, also unpaired, which in 
turn tapers into the spinal cord. 

Draw the brain from above, three times the natural 
size, naming the parts. 

Cut off the tops of the various regions of the brain. Do 
you find cavities (ventricles) in any of them? Can you 
find any nerves going from the brain? 

If no prepared skull is available, boil the head of another 
fish for a few minutes, and then pick away the flesh as 
far as possible with the forceps, taking care not to pull 
any of the bones from their proper positions. This will 
expose the skull, composed of numerous bones. See that 
these can be grouped in the following regions: 

(1) The opercular apparatus, consisting of the several 
bones composing the gill-cover (p. 24). 

(2) The facial portion, made up of the jaws and parts 
connected with them; numerous small bones around the 
eye, etc. See how the lower jaw is suspended from the 
skull. Does anything like this occur in man? 

(3) The cranium, consisting of a number of bones 
which form a box to enclose and protect the brain. 



COMPARISONS. 

Divide a page of vout note-book by a vertical line. 
Head one column Dogfish, the other Bony-fish, and in 
each column write the answers to the following questions, 
numbering them as they are here: 

(1) What kind of scales occur? 

(2) Where is the mouth? 

(3) What is the shape of the caudal fin? 

(4) Point out all the differences between the gills of 
the two. 

(5) Where are the nostrils? 

(6) Are the hard parts cartilaginous or bony? 

(7) Is there a spiral valve in the intestine? 

(8) Is there a swim-bladder? 

(9) Is there an operculum? 

After answering these questions read carefully the sec- 
tions on Elasmobranchs (pp. 322 to 325) and on Teleosts 
(pp. 326 to 336). 

Prepare another sheet as before with columns for dog- 
fish and bony-fish and answer the following questions: 

(1) Where does the animal live? 

(2) Is the surface of the body naked or scaled? 

(3) Is there a skeleton to the median fins? 

(4) Is there anything which could be called a hand or 
foot? Is the skeleton of the paired fins provided with 
knee, elbow, wrist, etc.? 

30 



COMPARISONS. 31 

(5) Do the nostrils connect with the mouth or throat? 

(6) What structures are used for respiration? 

(7) Where does the animal get its oxygen? 

(8) How many auricles and how many ventricles to 
the heart? 

Read all the matter upon fishes (pp. 317 to 336), includ- 
ing that already read, and decide to what order the bony-fish 
you dissected belongs. 



THE FROG. 

Each student should have an injected frog and a tadpole for 
dissection, a decalcified head for the study of the brain, and 
a large tadpole. If possible there should also be living frogs 
for study. The injection should be made through the ventricle 
which will fill the whole arterial system. Decalcified heads 
should be prepared by placing them in nitric alcohol about a 
week before they are to be used, and then washing them in 
running water for at least two hours. 

Skeletons are easily prepared * and there should be one for 
every three or four students. 

In the living frog notice the way in which the eyes 
can be retracted. Notice especially the way in which a 
frog breathes, observing the skin underneath the throat, 
and watching the nostrils through a hand-lens. On the 
back, a little in front of the vent, pulsations may be seen ; 
these are produced by a pair of lymph-hearts beneath the 
skin. 

* A skeleton may be quickly prepared by removing as much 
of the flesh as possible with scissors and scalpel, then boiling it 
with a little soap in the water, and picking away as much more 
flesh as you can, taking care not to separate the joints. Much 
better skeletons can be made by cleaning off the flesh and then 
soaking the frog for some weeks in water, brushing the parts every 
few days with a tooth-brush. If such a skeleton be soaked for a 
few days in a weak solution of glycerine and dried, it will retain 
its flexibility and usefulness for years. 

32 



THE FROG. 33 

In the prepared specimen notice the shape of the body. 
Can yon find scales anywhere? Is there anything like a 
tail? How many appendages are there? How do they 
compare with your own limbs? Open the mouth. Where 
do you find teeth? Where are the nostrils? Probe them 
with a bristle. Where does this appear in the mouth? 
How does the tongue differ from your own? 

Behind and a little below the eye is a circular tympanic 
membrane (connected with the auditory apparatus). Cut 
through this and insert a probe. Where does this appear 
in the mouth? With what does this Eustachian tube most 
nearly correspond in the shark? See the way the mouth- 
cavity narrows behind to form the gullet. In front of tlr's 
see the slit-like glottis in the floor of the mouth. 

In the fore limbs do you find parts corresponding to 
arm, forearm, wrist, palm, and fingers? How many 
fingers? In the hind leg do you find any parts besides 
thigh, shank, ankle, instep, and toes? If you have any 
difficulty, compare the way in which the joints bend with 
those in your own body, and find where your trouble is. 



Internal Structure. 

Beginning just in front of the vent, slit the skin forward 
in the middle line of the ventral surface to a point between 
the shoulders. Turn back the skin on either side. Is 
it firmly attached to the underlying muscles? Are there 
blood-vessels on its inner surface? Notice the muscles. 
Can you find any muscle-plates (myotomes, p. 17 or 25)? 

Next cut the muscles in the same way, a little to the 
(animal's) left of the middle line, carrying the incision 
forward through the hard parts between the shoulders, 
and taking great care to keep the underlying parts un- 



34 LABORATORY WORK. 

injured. This lays open the peritoneal cavity (ccelom). 
Insert a blowpipe into the gullet and innate the stomach. 
Is there any sharp boundary between it and the intestine? 
Is the intestine more or less coiled than in bony-fish or 
dogfish? Is it of the same size throughout? How is it 
suspended? 

Does the liver cover the stomach? Turn the liver for- 
ward and look for the greenish, spherical gall-bladder and 
the light-colored, lobulated pancreas. Do you find ducts 
from either of these to the intestine? Farther back, in 
the mesentery, near the enlarged portion (rectum) of the 
intestine, is the red spleen. At the posterior portion of the 
peritoneal cavity is the thin-walled urinary bladder. With 
what is it connected? 

Draw the digestive organs, showing the position of the 
deeper structures by dotted lines. 

Turn the intestines, etc., out of the body, exposing the 
reproductive organs and kidneys. These will differ in 
their appearance in the two sexes. 

In the male a yellowish, rounded body (testis) occurs on 
either side of the median line, and just in front of each 
are the yellowish, lobulated fat-bodies. Beneath (dorsal to) 
the testes are the reddish-brown kidneys, each having on 
its ventral surface a yellowish or golden adrenal gland. 

What is the shape of the kidneys? Are the testes and 
kidneys connected in any way? Do you find the ducts 
(ureters) leading back from the kidneys? Where do they 
end? 

In the female, the ovaries, crowded with dark-colored 
eggs, occur in the place of the testes, their size depending 
upon the season. Near them are the coiled oviducts. 
Trace these forward and back to their terminations. Do 
you find the fat-bodies? Do kidneys and adrenals corre- 



THE FROG. 35 

spond to the conditions described for the male? Are there 
ureters distinct from the oviducts? Draw the repro- 
ductive and urinary organs of your specimen. 

Insert a blowpipe in the glottis (p. 33) and inflate the 
lungs. What is their shape? Are they made up of little 
chambers {air-cells) throughout? 

Between lungs and liver is the pericardial cavity, and 
through its walls in the freshly killed specimen the beating 
of the heart can be seen. Open the pericardium very care- 
fully and expose the heart; make out the ventricle behind, 
and the auricles in front. Arising from the ventricle and 
crossing the auricles is the arterial trunk. Carefully clean 
this from the surrounding tissues and trace it to its divi- 
sion. Then follow each trunk. The right one soon di- 
vides into three branches; the anterior is the carotid, the 
middle the aortic arch, the third the "pulmonary artery. 
How does the trunk of the left side differ? 

Trace the carotid arch. Where does it go? What be- 
comes of the aortic arch? Do you find a dorsal aorta? 
On which side of the alimentary tract should the dorsal 
aorta be (p. 19)? To what organs is the pulmonary artery 
distributed? Do you find anything to compare with the 
ventral aorta (p. 18) and afferent and efferent branchial 
arteries? Draw the circulatory system as made out, viewed 
from the ventral surface. 

Place a drop of blood of the frog on a slide, cover it 
with a cover-glass, pressing it well down, and examine 
under the higher power of a microscope. What is the 
shape of the corpuscles? Are all alike in shape and size? 
Stain with fuchsin (see Introduction) and study again. 
Are all parts equally stained? 

Split the skin along the back and pull it away. Find the 
point where the head joins the back-bone; and beginning 



36 LABORATORY WORK. 

here, with a strong pair of scissors cut away the roof of the 
skull bit by bit, taking great care not to injure the brain 
This is easiest done on a decalcified specimen. Then in 
the same way cut away the neural arches of the vertebrae. 
This wil 1 expose the brain and spinal cord. The later 
work will be more easily followed if the animal be put for 
a day or more in 70% alcohol. 

In the spinal cord notice the spinal nerves given off at 
regular intervals on either side. How many are there? 
What relationship do they bear to the bodies of the verte- 
brae? Examine these spinal nerves more closely, and see 
if each is double (has dorsal and ventral roots) . Follow one 
out by carefully cutting away the bone, and see where the 
roots unite. Has either root an enlargement (ganglion)*! 
Look in the dorsal part of the body-cavity for these spinal 
nerves. Trace the posterior ones back to their union 
(plexus) to form the sciatic nerve going to the hind limb. 

In the brain, between the eyes, are the cerebral hemi- 
spheres. Are they separate? In front are the olfactory 
lobes. Are they separate? Behind the cerebrum, and at a 
lower level, is the 'twixt-brain. Next come the paired 
optic lobes, and behind them the medulla. What has 
become of the cerebellum (pp. 20, 29)? 

Sketch the brain and spinal cord from above, inserting 
all the nerves seen, and making the sketch twice the size 
of nature. 

Cut across the olfactory nerves and turn the brain back- 
wards. This will show the optic nerves arising from the 
region of the 'twixt-brain. Cut these as far as possible 
from the brain, and do the same with other nerves farther 
back, at last removing the brain from the skull. 

On its under surface trace the optic nerves back to the 
brain. Does the right nerve connect with the right optic 



THE FROG. 37 

lobe? Behind the optic nerves is a small projection, the 
pituitary body. How many nerves can ^ou find arising 
from the side of the medulla? 

With a sharp scalpel split the brain horizontally and 
examine the cavities found. Are they all connected? 
The larger cavities are called ventricles. Those in the 
hemispheres are the first and second, that in the 'twixt- 
brain the third, and that in the medulla the fourth. Are 
there ventricles in the optic lobes? Draw the brain, show- 
ing all cavities and connections found. 

In the prepared skeleton how many elements (vertebrce) 
do you find in the back-bone? Can you find neural and 
haemal arches (p. 27)? On either side of each vertebra 
find a transverse process. How do these compare with 
the ribs of a fish (p. 28)? Are they the same? Give the 
reasons for your conclusion. Notice the long bone (uro- 
style *) terminating the vertebral column. Connecting 
the hind limbs with the back-bone is the pelvic arch. Is 
it a true girdle? With what part of the vertebral column 
does it join? Connected with the fore limbs is the shoulder- 
girdle. Does it join the vertebral column? 

Extending along the median line below, in connection 
with the shoulder-girdle is the breast-bone, or sternum. 
How many parts in it? Are all equally hard? The part 
extending in front of the girdle is the omosternum, the 
xiphisternum projects behind. Connecting the breast-bone 
with the shoulder are two bones on either side; the ante- 
rior is the clavicle, the posterior the coracoid. Extending 
dorsally from the shoulder- joint is the shoulder-blade 
(scapula) , and above it the supra-scapula (partly cartilage) . 
At the junction of coracoid and scapula is the glenoid 

* This is composed of the coalesced caudal vertebrae of the tad- 
pole. 



38 LABORATORY WORK. 

fossa, in which fits the head of the first bone (humerus) of 
the arm. Has a joint like this much freedom of motion? 
The bone of the forearm is the radio-ulna. Does it show 
any signs of a double condition? With what does it con- 
nect below? How many bones in the wrist (carpus)? 
How are they arranged? How many in the palm (meta- 
carpus) and in each finger (digit)? How does the thumb 
differ from the others? 

On the outside of each half of the pelvic girdle is a 
deep cup (acetabulum), in which is the head of the thigh- 
bone (femur). Below this comes the tibio-fibula. Is this 
double? Below this comes the ankle region (tarsus). The 
first two bones of this are long, the second very short. 
What effect does this have on the position of the heel 
(p. 33)? Compare the tarsus with the carpus. Is there 
anything which you could call a sixth toe? Does it come 
on the inside or outside of the foot? 

In the skull make out an axial portion (cranium) ex- 
panding in front and behind to support a bony arch 
below the eye, and attached to the cranium behind, the 
lower jaw (mandible). At the posterior end of the skull 
is the large opening (foramen magnum) through which the 
spinal cord connects with the brain. On either side of the 
foramen is a protuberance (occipital condyle) by means of 
which the skull articulates with the first vertebra (atlas). 
These condyles are borne on the exoccipital bones, the rest 
of the border of the foramen is formed of cartilage. (In 
most vertebrates the foramen is closed below by a basi- 
occipital, above by a supraoccipital, bone.) 

The dorsal surface of the cranium is formed of a pair of 
fronto-parietals behind, and in front of them an unpaired 
sphenethmoid bone. Next come a pair of nasal bones, 
their major axes transverse to that of the skull. In front 



THE FROG. 39 

of the lateral end of the nasals are the nostrils, while the 
median ends join the pair of premaxillary bones, which 
form the tip of the upper jaw. 

At the posterior part of the fronto-parietal a prootic bone 
extends laterally, forming the roof of the internal ear and 
meeting laterally a T-shaped squamosal bone; the long 
arm of the T extending downwards and backwards to- 
wards the angle of the jaws, a small cartilage (the quadrate) 
intervening between the squamosal and the lower jaw. 
The upper jaw is formed of a short splint-like quadrato* 
jugal, which connects behind with the quadrate and in 
front with the long, tooth-bearing maxillary bone, and is 
completed in front by the premaxillaries already referred 
to. Extending forward and downward from the lower 
anterior surface of either prootic, and extending a branch 
backwards to the quadrate, is the pterygoid bone, which 
joins the maxillary in front, near the lateral end of the 
nasal bone. Draw a view of the skull from above three 
times natural size, naming the parts. 

In the ventral view of the skull make out the exoc- 
cipitals, prootics, sphenethmoid, premaxillaries, maxil- 
laries, and quadra to jugals as before and see that a large 
part of the floor of the cranium is composed of an unpaired 
parasphenoid bone which overlaps the sphenethmoid in 
front. Beneath and parallel to the nasals are a pair of 
palatine bones and in front of them and separated from 
them by a short distance are a pair of teeth-bearing 
vomers. Draw a ventral view of the skull. 

The lower jaw is composed of a pair of mento-Meckelian 
bones which meet in front, followed by a short dentary, 
the posterior end of which is grasped on the inner side by 
an angular e, which extends back to the angle of the jaw. 
Notice that on the upper outer side of the angulare a 



40 LABORATORY WORK. 

cartilage (Meckel's cartilage) is visible and that the articu- 
lation of the lower jaw with the quadrate is formed by 
the posterior end of this cartilage. Draw a side view of 
the skull, including the lower jaw, naming all the parts 
visible. 



THE TADPOLE. 

If possible the pupils should have a chance to examine 
tadpoles of different ages. These can readily be obtained by 
collecting the eggs in the spring and allowing them to hatch 
out in glass jars. A number of these can be killed at various 
stages by means of picrosulphuric acid (see Introduction) used 
for a couple of hours, then washed two to three hours in water, 
and preserved in 70% alcohol. The earliest stage necessary 
should show the external gills; the latest, which are more 
easily obtained from the ponds, should have the hind legs well 
formed. 

In the earliest of these larvae the pupil should pay 
especial attention to the gills. How many are there? 
Are they fringed? How do they differ from the gills of 
fishes? What is the relative size of head, body and tail? 

In the older larvse the jaws should be examined. What 
is their nature? What is the size of the mouth compared 
with that cf the adult? On the left side of the body see 
the opening of gill-chamber. Is there one on the right 
side? Carefully open this chamber, taking great pains not 
to cut too deeply. Do the right and left sides of the gill- 
cavity connect? Can you find any traces of the fore 
limb? Carefully open the abdomen and notice the com- 
pact coiling of the intestine. Is it relatively longer or 
shorter than in the adult?" Examine the tail with its fin. 
Is there a skeleton to the fin? Is the tail homocercal or 

41 



42 LABORATORY WORK. 

heterocercal? Pick away the muscles from one side of 
the body until the middle line of the body is reached. 
Do you find any vertebrae? Lying in this median fine 
find a continuous gelatinous cord, the notochord. 



COMPARISONS. 

Prepare a sheet of paper with two columns as before, 
one for Fishes and the other for the Frog and Tadpole, and 
give answers to the following questions: 

(1) Is the skin naked or scaly? 

(2) What kind of appendages occur? 

(3) Is the pelvic girdle united to the back-bone? 

(4) Is there a Eustachian tube? 

(5) What differences are there in the heart? 

(6) What are the organs of respiration? 

(7) Do the nostrils communicate with the mouth? 

(8) Differences between transverse processes and ribs? 

(9) Is a sternum present? 

Read the section on Amphibia (pp. 336 to 341) and 
compare this with the account of the fishes already studied. 

On another sheet rule two columns for Fishes and 
Amphibia and answer the following questions, using your 
notes and the sections which you have read to aid in 
certain points: 

(1) Is the blood cold or warm? 

(2) Are median fins present in young or adult? 

(3) Are gills present in young or adult? 

(4) Are lateral-line organs ever present? 

43 



THE TURTLE. 

Any common species of turtle will answer for the laboratory 
work. For making out the points mentioned below injection 
is not necessary. Living specimens may be killed for dis- 
section with chloroform or ether. If not to be used immedi- 
ately the plastron should be removed as soon as the animal is 
killed, so as to permit free entrance of the preservative fluid. 

External. 

The hard shell is composed of a dorsal portion, the 
carapace, and a flat ventral shield, or plastron. Are the 
plates covering these arranged in the same way on both? 
How are carapace and plastron united? Are head, legs, 
and tail naked? How many toes on the feet? Are claws 
present? Open the mouth. Are teeth present? Are 
there lips? Is there a tongue? Do the nostrils connect 
with the mouth? At the inner angle of the eye see a fold, 
the nictitating membrane. Pull it out with the forceps. 
What purpose can it fulfil? Is there an external ear? 

Internal, 

Open the body by sawing the hard parts connecting 
carapace and plastron on either side, then cut the skin, etc., 
from the plastron and remove that plate, leaving the ani- 
mal in the carapace. This exposes the muscles and the 

44 



THE TURTLE. 45 

limb-girdles, and, after the removal of a thin membrane, the 
viscera. Was either girdle fastened to plastron? Just 
behind the shoulder-girdle is the heart, and on either side 
of this the dark liver. In the left lobes of the liver is the 
stomach. Trace the intestine to the vent. Is there an 
enlarged terminal portion? Is the intestine supported by 
a mesentery? Do you find pancreas or spleen? Turn the 
liver inwards and see the lungs. Are they large? 

In the heart how many chambers? From the front see 
the vessels. Trace them out, making out carotids, aortic 
arches, and pulmonary arteries, comparing your work step 
by step with the frog. What differences do you find 
between right and left aortic arches when traced to their 
junction with the dorsal aorta? 

In the body-cavity, behind, are the kidneys. Are they 
smooth or lobed? Where do their ducts empty? Do you 
find a urinary bladder arising from the intestine behind? 
The ovaries are a broad oval, and can usually be recognized 
by the contained eggs. Where do the oviducts empty? 
The testes are smaller, long oval, and are outside and behind 
the kidneys. 

In the skeleton * look for the vertebral column on the 
inside of the carapace. Is it firmly united to it? Can you 
find any traces of ribs? If so, in what respects are they 
peculiar? What parts can you recognize in the shoulder 
and pelvic girdles? In either limb, beyond the humerus 
or femur, make out two bones {radius and ulna in the fore 
limb, tibia and fibula in the hind linib), and beyond this 
the (how many?) carpal or tarsal bones. How does this 
explain certain peculiarities in the frog? Draw either 

* Skeletons sufficient for these purposes can readily be made by 
boiling the specimens and washing away the flesh with the aid of 
a nail-brush. It is well to boil the head separately. 



46 LABORATORY WORK. 

limb, naming parts, remembering that the radius is on 
the side of the thumb, the tibia on that of the big toe. 

In the skull is the socket (orbit) of the eye completely 
enclosed in bone. How does the lower jaw join the skull? 
What is the means for articulation of the skull with the 
vertebrae of the neck? Are the vertebra of the neck hol- 
low in front, behind, or on both surfaces? Examine each 
and decide which ones are amphicoslous (p. 27), which 
proccelous (hollow in front), which opisthoccelous (hollow 
behind), and which will fit none of these categories. 



SNAKE. 

Are there any traces of limbs? Can you divide the body 
into head, neck, thorax, and tail? If so, give reasons for 
the divisions you recognize. What is the character of the 
skin? What marked difference exists between the skin of 
the head and that of the body? Are the dorsal and ven- 
tral surfaces alike? Where is the vent? Examine a scale 
carefully. Is there any skin outside it? Can you pull the 
scales away from the body? Does a snake shed its skin? 

Examine the head. Open the mouth. Are teeth present, 
and, if so, where? See the tongue. What is its character? 
Pull it out with the forceps. Can it be protruded when 
the mouth is shut? 

47 



BIRD. 

The following account will apply to almost any common 
bird. The English sparrow or the pigeon is -possibly the most 
convenient. 

External. 

Notice that the body presents the regions, head, neck, 
trunk, and tail. How many paired appendages are found? 
What covers the body? what the legs and feet? 

In the head notice the beak, composed of upper and 
lower mandibles. With what is it covered? Is the upper 
mandible movable? Open the mouth; do you find teeth? 
What is the shape of the tongue? Where are the nostrils? 
Do they connect with the mouth? Behind the tongue, on 
the floor of the mouth, will be found the glottis (p. 33). 
How many eyelids do you find? Look at the inner corner 
of the eye for the nictitating membrane. Pull it out with 
the forceps. Is it like the same structure in the turtle? 
Hunt among the feathers for the ear-opening. Are the 
feathers around it different from the others? 

Extend the wing. Can you find parts corresponding to 
arm, forearm, and hand? Are the feathers alike in all 
parts? * How much is the surface of the wing increased 
by the feathers? 

* The feathers on different parts of the wing have special names. 
The long quills on the hand are primaries; on the forearm, seconda- 

48 



BIRD. 49 

Are the feathers essentially alike on all parts of the 
body? Are all parts equally well covered? Pull out a 
large wing-feather and notice the central axis or shaft sup- 
porting the expanded portion or vane made up of small 
side-branches (barbs), and these in turn having smaller 
branches (barbules). Pull two of these barbs apart, watch- 
ing with a lens to see the part played by the barbules. 
Are the conditions the same at the base of the vane? Can 
you find a downy feather among the others? Examine it 
carefully and see how it differs from the quill described. 
Pick the feathers from a part of the breast and study one 
of the pin-feathers. What parts occur in it? 

Next pick the feathers from the whole bird. This will 
be more easily done by dipping it in hot water. When 
picking the feathers notice that they come from pits in the 
skin. When the bird is picked, look for these pits. Are 
they equally distributed on all parts of the body, or are 
they arranged in feather-tracts f 

In the leg see the thigh and shank (drumstick). Where 
is the heel? Does the bird walk on the whole foot? Con- 
necting the shank with the toes is the tarso-metatarsus. 
How many toes? Do they all point the same way? 

Internal Structure. 

Cut through the skin in the median line below from the 
neck to the vent, being careful not to injure the deeper 
structures in the neck. Pull the skin away. Insert a 
blow-pipe in the mouth and innate. This will render the 

ries; and those on the arm, when they occur, are tertiaries. The 
short feathers overlapping the large quills above and below are 
the upper and lower wing-coverts. At the bend of the wing, just 
outside the primary coverts, are short quills, borne on the thumb 
and forming the false wing (ala spuria). 



50 LABORATORY WORK. 

oesophagus very evident, and will show a specialized en- 
largement, the crop, if it exist. In front of the oesophagus 
is the ringed trachea, or windpipe, while on either side are 
veins (jugulars) usually gorged with blood. 

Cut through the abdominal walls in the median line 
from the breast-bone to the vent. Open, and, after inflat- 
ing as before, notice the air-sacs. How many do you find? 

Next remove the limbs from one (the left) side, cutting 
the muscles away from the keel of the breast-bone. Then 
cut through the ribs where they join the breast-bone, and 
next sever them near the back, removing the walls of the 
body from one side. This will expose the reddish-brown 
liver, and, partially covered by it, the muscular stomach or 
gizzard; farther in front and near the back-bone the lungs, 
and in other parts the coils of the intestine. After draw- 
ing the viscera in position, proceed with the dissection. 

Pull the gizzard back and inflate, this time through 
the oesophagus in the neck. Where is the glandular 
stomach (proventriculus)? Where does the intestine con- 
nect with the gizzard? Is the intestine the same size 
throughout? Is a mesentery present? 

In front of the liver is the pericardium containing the 
heart. Open the pericardium and trace, as far as possible 
without injection, the blood-vessels going from it. Make 
out the carotids, aortic arch, and pulmonary arteries. 
How many of each? Which way (right or left) do they 
turn? Cut out the heart, and cut it open horizontally. 
How many chambers are found? Sketch the circulation 
as far as made out. 

In the hinder part of the body-cavity are the dark-colored 
kidneys. Are they irregular in outline? In front of them 
are the reproductive organs. The testes are whitish and 
oval ; the ovaries in the breeding season are filled with eggs 



BIRD. 51 

in various stages of growth. Can you trace the ducts from 
either kidneys or reproductive organs? Where do they 
end? Are the reproductive organs paired? 

Open the skull very carefully, beginning at the top and 
working down on the sides. If the head be cut off and 
put in alcohol for twenty-four hours or more after opening 
the skull, the parts of the bram will be better made out. 
In front are the cerebral hemispheres, with the olfactory 
lobes showing in front and below. Inserted in the angle 
between the two hemispheres is the cerebellum, and on 
either side of the latter, and partially covered by the 
cerebrum, are the optic lobes. What has become of the 
'twixt-train? Do you find the medulla? Are all the 
parts of the brain smooth? Draw the brain from above 
and from the side. 

The essential features of the skeleton can be made out 
from the same specimen after boiling. The parts neces- 
sary are the head, the shoulder-girdle, wing, leg, and a 
few of the vertebra?. What is the shape of the ends of 
the vertebrae? In the shoulder-girdle what parts can you 
recognize? What name must be given to the wish-bone, 
or furculaf (compare the frog). In the wing humerus, 
radius, and ulna are readily made out. How many carpal 
bones do you find? In the 'hand' how many fingers can 
you distinguish? Sketch the carpus and 'hand/ with the 
ends of radius and ulna. In the leg recognize femur, 
tibia, and fibula. Where is the heel? What must the 
bone above the toes be? 

Are the bones distinct in the skull? Move the beak 
upon the skull. Where do the bones slide? Connecting 
the angle of the upper jaw with the skull is the quadrate 
bone. Is it movable? 



COMPARISONS. 

With two columns, one for Bird, the other for Turtle 
and Snake, answer the following questions: 

(1) Is the blood warm or cold? 

(2) Are feathers present? 

(3) Are there any wings? 

(4) Is there an elongate true tail? 

(5) Are the carpus and tarsus long or short? 

(6) Are air-sacs present? 

(7) How many aortic arches? 

(8) How many ovaries? 

Read the accounts of Reptiles (pp. 342 to 350) and 
Birds (pp. 350 to 363). 

On a second sheet, with columns for Birds and Reptiles, 
answer the following questions: 

(1) Are scales present? 

(2) Are claws present? 

(3) How many occipital condyles? 

(4) Is there a distinct quadrate bone connecting the 
upper jaw with the skull? 

(5) Are true ribs present? 

(6) How many chambers to the heart? 

(7) What is the size of the eggs? 

(8) Are functional gills ever developed? 

(9) Do the urinary and reproductive ducts empty into 
the hinder part of the alimentary canal? 

Read the account of the Sauropsida (p. 342). 

52 



RAT. 

If possible each student should be provided with two speci- 
mens, one injected, the other not. If rats are not easily ob- 
tained, a single injected specimen will suffice. The injection 
is easiest made by removing the skin on the inner side of the 
thigh, exposing the femoral artery and vein. The canula can 
be inserted in these, pointing towards the head, and the whole 
of both arterial and venous systems filled. Only a small amount 
of injecting fluid is necessary, and care should be taken not to 
break any of the vessels by too great pressure. For the study 
of the heart and brain it is well to provide each student with 
these parts from some larger animal like a sheep, hardening 
and preparing them some time before they are to be used. 

External. 

With what is the body covered? Is there hair on the 
tail? Do you find scales on the tail? In what respect 
do they resemble and in what differ from those of reptile 
or fish? 

How many toes on the fore feet? Do you find any 
trace of a thumb? Are the toes provided with claws? 
Sketch the sole, bringing out the callous spots. How 
many toes in the hind foot? Sketch the sole and com- 
pare with that of fore foot. 

How many nostrils? Of what use to the animal are the 
'whiskers' of the upper lip? Examine eyes and look for 

53 



54 LABORATORY WORK. 

third eyelid at inner angle of the eye. Does it resemble 
any structure you have found in the animals previously 
studied? Is there anything similar in your own eye? 

Internal. 

Cut the skin along the ventral median line from near 
the vent to a point behind the jaw. Lay the skin back, 
separating the loose connective tissue which binds it to the 
deeper parts. See the thin muscles covering the abdo- 
men. Do they show any signs of segmental repetition? 
(cf. Frog). Feel for the breast-bone, and open up the 
body by cutting through muscular walls from between 
hind legs to breast-bone. Make transverse cuts on either 
side and fold the walls outwards. This opens the perito- 
neal cavity. In this, without disturbing parts, can now 
be seen, in front, the dark-colored liver, behind this the 
coils of the intestine, and between the hinder coils of this 
tube the urinary bladder. 

Tip the liver to your left and find the stomach. Sketch 
from the side, showing the entrance of the gullet {esopha- 
gus) and the beginning of the intestine. Notice how liver 
and stomach are connected by thin membrane (mesentery). 
Tip the stomach forward and notice the spleen suspended 
in another portion of the mesentery. 

Trace the intestine, without cutting anything. It is also 
held by its mesentery. It makes first a large loop back- 
wards (duodenum) and then comes forward to form numer- 
ous convolutions. Find a large pocket (c&cum) given off 
from the intestine. All of the tube in front of this is 
called the small intestine; back of it the large intestine. 
In the latter two portions — (1) colon, (2) rectum — can 
readily be distinguished by the different appearance of 
the walls. 



RAT. 55 

Spread out a portion of the mesentery supporting the 
intestine and notice in it small vessels. Some of these 
will be found to be single, others, two close together. The 
double vessels are arteries and veins. They can be dis- 
tinguished by tracing them towards the middle line of 
the body. The veins unite in a large vein {mesenterial 
vein) which follows along the colon, thence into an anterior 
fold, where it is joined by other veins (gastric) from the 
stomach and (splenic) from the spleen. From the union 
of these is formed the portal vein, which enters the liver 
from behind. The small arterial branches arise from a 
mesenterial artery which accompanies the mesenterial vein 
for some distance and then can be traced back to the 
median line of the dorsal surface of the body-cavity, 
where it joins the great arterial trunk, the aorta. From 
the aorta, just in front of the origin of the mesenterial 
artery, arises the cceliac axis or artery, which gives off a 
branch to the liver (hepatic artery), and then divides into 
splenic and gastric arteries, going to the spleen and stom- 
ach respectively. Trace these arteries. Where does the 
hepatic enter the liver? 

The single vessels in the mesenteries are the lymphatics. 
Their purpose is to carry the products of digestion for- 
ward and eventually empty them into the blood-vessels. 
These lymphatics unite in a lymphatic duct, which runs 
closely parallel to the mesenterial artery and empties into 
a thoracic duct running parallel with the aorta. 

Sketch the blood-vessels (X2) so far made out on a 
sheet large enough to accommodate the whole circulatory 
apparatus of the rat. 

In the mesentery supporting the duodenum find the 
fatty-looking, irregular pancreas. Where does its duct 
enter the intestine? 



56 LABORATORY WORK. 

How many lobes are there in the liver? Are they sym- 
metrically placed? Beside the portal vein and the hepatic 
artery is the bile-duct. Trace it forward and see how its 
branches arise from the liver-lobes. Trace it backwards 
and see where it enters the intestine. Look on the posterior 
surface of liver for the gall-bladder. Tip the liver towards 
the tail. See how it is attached by mesenteries to a 
muscular partition (diaphragm) bounding the peritoneal 
cavity in front. See the oesophagus and a blood-vessel 
(postcava) extending from the liver through the dia- 
phragm. Sketch the alimentary canal. 

Cut through the oesophagus just in front of the stomach 
and through the rectal portion of the intestine, and cutting 
the mesentery close to the intestine remove the alimentary 
canal. 

In the body-cavity see, dorsal to the liver, the kidneys. 
Are they at the same level? Covering the anterior end of 
each kidney is a triangular supra-renal capsule. Trace 
from each kidney (median surface) backwards a whitish 
tube, the ureter. In the median line of the body-cavity is 
the aorta already mentioned. Trace it backwards, finding 
the arteries (renal) going to the kidneys. Farther back 
the aorta divides into a pair of common iliac arteries. 
Trace these into the legs. Do you find them to divide? 

Just behind the point of division of the aorta into the 
common iliacs can be seen the common iliac veins, which 
return from the legs and unite into a vessel, the postcava, 
which passes forward, at first dorsal to the aorta. A little 
farther forward the postcava receives an ileo-lumbar vein 
from each side, and then a renal vein from each kidney. 
From the kidneys trace the postcava forward" through the 
liver. This may readily be done by cutting away the ven- 
tral part of the liver and then, inserting the point of the 






RAT. 57 

scissors into the postcava, make a cut. Continue this 
until the whole vessel is laid open up to the diaphragm. 
On the inner surface of the postcava, inside the liver, 
notice the openings of the hepatic veins. These bring to the 
postcava the blood which entered the liver by the portal 
vein. 

Add these parts to the sketch of the blood system 
already begun. 

With a sharp scalpel split a kidney horizontally. In the 
cut section make out on the median side a cavity (the 
pelvis of the kidney) from which arises the ureter. Into 
the pelvis a papilla projects from the outer wall. In the 
thick outer wall notice the difference in appearance 
between the outer cortical substance and the more central 
medullary substance. Sketch the cut section. 

Notice the direction of the muscle-fibres in the dia- 
phragm. What would be the effect of their contraction 
upon the diaphragm? * Cut through the diaphragm ven- 
tral to the postcava and continue the cut forward along 
the ventral surface of the body to one side of the median 
line. Cut the ribs with stout scissors. This will lay open 
the pleural cavity. 

In the pleural cavity, behind, will be seen the postcava, 
and dorsal to it the oesophagus. These pass forward 
between the lobes of the lungs. Notice the thin mem- 
brane (mediastinum) passing dorsally from the breast- 
bone towards the heart and lungs. The heart itself will 
be found to be enclosed in its own thin sac {pericardium). 
Sketch the contents of pleural cavity. 

* An instructive demonstration can be made by opening the 
abdominal cavity of some small mammal in which the diaphragm 
is so thin that the lungs are seen in outline through it. Then 
puncture the diaphragm and note the effect on the lungs. 



58 LABORATORY WORK. 

Cut open the pericardium and study the heart. Its apex 
is directed backward and to the (animal's) left; its broader 
base in front and to the right. Tip the heart to your right, 
and notice how the postcava enters it near the base on the 
right side. Just before its entrance into the heart it 
receives a similar vessel (the right precava) from in front, 
while the left precava, passing behind the heart, enters it 
from the side. Follow the precavse forward, cutting 
away the fatty-looking thymus gland just in front of the 
heart in order to trace the vessel. Soon each divides into 
a jugular vein (right and left) and a subclavian vein, the 
former going forward in the neck, the latter into the fore 
limbs. Trace the jugulars forward to head; do they 
divide? Insert precavse and their branches as well as 
anterior end of postcava in the sketch of the blood-vessels. 

Arising from the left side of the base of the heart is the 
aortic arch. Follow this forward; to which side of the 
body does it turn? From the arch of the aorta trace the 
following vessels: (1) Right brachiocephalic artery, which 
soon divides into the right subclavian artery and the right 
common carotid artery. Follow the subclavian into the 
limb, and the common carotid towards the head. Where 
does the common carotid divide into internal and external 
carotids f (Just outside the common carotid will be found 
a white thread-like nerve. It is the vagus (pneumogastric) 
nerve, which supplies the stomach, heart, and lungs.) 
(2) The left common carotid; and (3) close to it in its 
point of origin from the aortic arch the left subclavian 
artery. Trace these as before. Do you notice any differ- 
ences between these vessels on the two sides of the body? 

Tip the heart to your left and trace the course of the 
aorta from the origin of the left subclavian back to the 
origin of the cceliac artery already found. On which side 



RAT. 59 

(dorsal or ventral) of the oesophagus does the aorta lie? 
On which side is the heart, and on which side does the 
aortic arch pass? Insert the vessels now made out in the 
sketch, which should now represent the principal vessels 
of the systemic circulation. 

Dissect the aortic arch loose from the surrounding 
tissue, lift it up, and see dorsal to it the pulmonary arteries 
going to the lungs. From what part of the heart do they 
arise? Tip the heart to the animal's right and see the 
pulmonary veins, which bring the blood back from the 
lungs to the heart. On which side, with reference to the 
pre- and postcava, do they enter the heart? The pul- 
monary arteries and pulmonary veins belong to the pul- 
monary circulation. Add them to the sketch. 

Cut through the cavse, pulmonary vessels, and aorta, and 
remove the heart.* The heart is conical in shape, with a 
broader anterior base and a more pointed posterior apex. 
On the base on either side will be found small lobes — 
the auricles. Split the heart parallel to the horizontal 
plane of the animal with a sharp scalpel, keeping in mind 
which side of the organ was originally right and which 
left. Make out two pairs of cavities (usually containing 
clotted blood, which should be carefully removed). Which 
of these have the thicker walls — the right or the left? 
The basal cavities are the auricles, the apical the ventricles. 
Which parts, auricles or ventricles, would you suppose to 
play the greater part in forcing the blood through the 
circulation? Study the connections between auricles and 
ventricles. Do the two auricles connect with each other? 
Is the same true of the ventricles? Notice what vessels 
enter the left auricle. Where do the pre- and postcaval 

* The larger heart of a cat, sheep, or pig will show these points 
much better. 



60 LABORATORY WORK. 

enter? Where does the blood go from the left ventricle? 
Insert a diagram of the heart, with its chambers, in the 
sketch of the circulation. 

Between the common carotids is the ringed trachea, or 
windpipe. Dissect it loose and cut near the head. Insert 
a blow-pipe in the hinder portion and innate the lungs by 
blowing. Are the rings of the trachea complete? Trace 
the trachea forward and notice enlarged anterior portion 
(larynx), and just in front, and ventral to it, the hyoid 
bone. Beneath the trachea (dorsal to it) is the oesophagus. 

Remove the skin from the head. Notice the large 
muscles attached to the jaw, and just in front of the ear 
the salivary (parotid) gland. - Cut through the jaw muscles, 
and, beginning at the angles of the mouth, carefully cut 
backwards through the cheeks, so as to .allow the lower jaw 
to be bent back. In the mouth-cavity study the teeth. 
In front are the incisors, and further back the molars. 
Notice the large gap (diastema) between them. How many 
of each kind in each jaw. With a knife test the hardness 
of the front and back surfaces of the incisors. Which is 
the harder? Why are these teeth always sharp? Is there 
any such arrangement in the molars? 

Between the molars is the hard palate, its surface with 
transverse folds. Farther back is the soft palate, bounded 
behind by the place (internal narial opening) where the 
nostrils communicate with the back part of the mouth- 
cavity. How many of these openings do you find? Slit 
soft palate with the scissors and see how this arrangement 
is brought about. 

Opposite the internal narial opening (i.e., on the floor 
of the pharyngeal region) is an opening — the glottis, sur- 
rounded by a raised rim, which is enlarged in front into 
a soft epiglottis. Inside of the glottis may be seen two 



RAT. 61 

folds {vocal chords), which narrow the opening. Insert a 
probe into the glottis. Where does it appear? 

Split the skin down the back and remove it from the 
body, and then with the bone forceps break through the 
cranial walls at the back of the head,* taking pains not to 
injure the underlying structures. When the opening is 
made enlarge it by removing the skull bit by bit with a 
strong knife from the dorsal surface and right side. Then 
continue the process back in the neck region as far as the 
shoulders until the brain and anterior part of the spinal 
cord are exposed. 

In the brain, viewed from above, make out in front the 
olfactory lobes, next the large cerebrum, and behind this 
the cerebellum, and following the cerebellum the medulla 
oblongata, broad in front and tapering behind into the 
spinal cord. Are any of these parts paired? The line 
between medulla and spinal cord is not a sharp one, and 
the place of passage through the skull may be regarded as 
the boundary. Sketch these parts in outline from above 
and from the side, X2. 

Over the whole brain is a rather tough membrane, the 
dura mater, which is next to be removed from the dorsal 
surface. Do you find any convolutions on the cerebrum? 
Cut through the olfactory lobes as far forward as possible 
and lift the cerebrum very carefully from in front. It 
will be found to be tied by the optic nerves, going from 
the ventral surface. Cut these as close to the skull as pos- 

* The points relating to the brain can be made out more easily on 
the cat or sheep, but with a little pains the directions here given can 
be followed on the rat. In the case of these larger forms the brain- 
cavity should be opened and the whole head be placed in some 
hardening fluid (Miiller's fluid, formol, or alcohol) some days before 
the laboratory exercises. 



62 LABORATORY WORK. 

sible. Do the olfactory lobes arise from the tip of the 
cerebrum? Roll the brain very carefully to the left side, 
looking at the same time at the right side of the medulla 
for nerves. From its anterior angle (below the cerebellum) 
will be found a strong nerve, the trigeminus, and just 
behind it another nerve, the facial and auditory com- 
bined. Some distance farther back, yet still inside the 
skull, arises a more complex nerve, consisting in reality 
of three, the glossopharyngeal, the vagus, and the spinal 
accessory. (Thus we can easily make out in the rat the 
following nerves: i, olfactory; n, optic; v,.. trigeminal; 
vu, facial; viii, auditory; ix, glossopharyngeal; x, vagus 
or pneumogastric ; xi, spinal accessory. The other nerves 
are not easily seen on so small a form.) 

Tip the cerebrum forward, and notice between it and the 
cerebellum the optic lobes behind and the 'twixt-brain in 
front. How does this compare with what was found in the 
dogfish? Tip the cerebellum forward and see the large 
triangular opening in the roof of the medulla. 

On the lower surface of the brain see the cut optic 
nerves. From which division of the brain do they arise? 
Behind the optic nerve find a median lobe, the hypophysis 
or pituitary body. 

With a sharp scalpel make a series of cross-sections 
through the cerebrum. Are the two halves completely 
separate? In each half find a cavity (ventricle), and above 
it in the solid tissue a transverse lighter band (corpus 
callosum). Draw the section. Make similar sections 
through the 'twixt-brain and the optic lobes. How many 
cavities do you find here? Draw each section. 

Cut a longitudinal vertical section through the cerebel- 
lum to left of median line, and notice the way in which the 
cerebellum is folded. The somewhat bush-like structure is 



RAT. 63 

known as the arbor vitas. Make a sketch of it. Cut 
transversely through the rest of cerebellum and medulla, 
and in the section see the folds of cerebellum cut in the 
opposite direction, and, below, the thick floor of the 
medulla. Cut through the medulla farther back. Do 
you find a central canal in the section? 

On the ventral surface of the neck, just outside the caro- 
tids, dissect away carefully, keeping the fore legs stretched 
out, until you find nerves (white cords) going from the ver- 
tebral region to the sides of neck. Can you make out two 
roots to each nerve? Just in front of the ribs notice that 
the nerves are larger, and that they go to the fore limb just 
in front of subclavian artery and vein. How many of 
these nerves as they arise from the neck interlace to form 
the brachial plexus (the network from which the limb 
nerves arise). Trace them into the limb. Sketch the 
plexus. 

Separate the muscles in the bend of the knee, exposing 
the large sciatic nerve. Trace the nerve backwards towards 
the trunk. Does it pass through any bones? Trace the 
nerve inside the dorsal wall of the body-cavity. Do you 
find a plexus like that of the fore limb? If so, how many 
nerves enter into its formation? 



COMPARISONS. 

With three columns, for Ichthyopsida, Sauropsida, and 
Rat respectively, answer the following questions: 

(1) Is hair present? 

(2) Do you find true scales or feathers? 

(3) Is there an external ear? 

(4) Do you find anything like gill-slits? 

(5) How many chambers in the heart? 

(6) How many aortic arches? 

(7) Do the aortic arches bend to the right or to the left? 

(8) Is a diaphragm present? 

(9) Do they produce eggs? 

Read the account of the Mammalia (pp. 363 to 392). 

64 



COMPARISONS. 

With five * columns, one for Fish and Dogfish, one for 
Frog, one for Turtle and Snake, and one each for Bird 
and Rat, answer in a detailed manner the following ques- 
tions : 

(1) Is the body bilaterally symmetrical? 

(2) Are paired appendages present? 

(3) How many nostrils? 

(4) How many eyes? 

(5) How many ears? 

(6) Are the skeletal parts external or internal? 

(7) Is the vent dorsal or ventral? 

(8) Is there a skull? 

(9) In what plane do the jaws move? 

(10) Is the back-bone a single structure? If not, of 
what is it composed? 

(11) Are both shoulder- and pelvic-girdles present? 

(12) On what side of the alimentary canal is the central 
nervous system? 

(13) What parts are found in the central nervous system? 

(14) To what organs do the first pair of nerves go? 

(15) To what organs do the second pair of nerves go? 

(16) How many and what parts do you find in the brain? 

* In case one or more of these forms are not studied the columns 
will be correspondingly less in number. 

65 



Ob LABORATORY WORK. 

(17) Are there cavities inside the brain? 

(18) Is there a peritoneal cavity? 

(19) In what way is the alimentary canal supported? 

(20) Do you find in each form liver, spleen, and pan- 
creas? 

(21) In what part of the cavity do you find the kidneys? 

(22) What cavity surrounds the heart? 

(23) What chambers do you find in the heart? 

(24) Is the heart dorsal or ventral to alimentary canal? 

(25) Is the aorta dorsal or ventral to alimentary canal? 

(26) What vessels carry blood to the head? 

(27) Are the respiratory organs connected, either di- 
rectly or indirectly, with the alimentary canal? 

(28) Are any parts (if so, what) repeated one after an- 
other in the body? 

(29) Draw a diagram of a transverse section through the 
body in the region of the heart, showing the heart, spinal 
cord, oesophagus, vertebra, aorta, and body-walls. 

(30) Draw a similar section through the kidneys, show- 
ing the peritoneal cavity, intestine, mesentery, spinal cord, 
kidneys, aorta, vertebra, etc., and the body-walls. 

Read the whole account of the Vertebrata (pp. 290 to 
392), re-reading those parts already read. 



CRAYFISH OR LOBSTER. 

Each pupil will require at least two specimens. One of 
these should be opened along the back, as described below, and 
placed for some days in alcohol in order that the internal parts 
may become hardened, thus better fitting them for dissection. 
Injection is easiest performed by cutting into the dorsal surface 
of the abdomen and inserting the canula into the dorsal abdom- 
inal artery and injecting forwards. This specimen preserved 
in alcohol will answer for all internal structures. 

External. 

Can you distinguish two regions in the body? How 
many joints (segments, somites, or metameres) can you 
distinguish in the posterior region or abdomen? Can you 
see somites in the anterior region (cephalothorax)? 

Examine a somite (the third) of the abdomen. How 
is it joined to the somites in front and behind? Are the 
parts between the somites as hard as the walls of the 
somite? What is gained by this arrangement? How does 
the wall of the somite differ from a ring? To what part 
of the ring are the appendages (swimmerets) attached? 
How many of these are there on the somite? In a swim- 
mer et make out the basal joint (basiopod), having two 
leaf -like branches, one towards the median line of the 
body (endopod), the other outside of this (exopod). Draw 
the somite and appendages from in front. 

67 



68 LABORATORY WORK. 

Compare the somites behind the third with that one. 
Do all have the two-branched appendages? How are the 
swimmerets of the sixth somite modified? How does the 
last somite (telson) differ from the others? Where is the 
vent? Compare the appendages of the first and second 
abdominal somites with those of the third. In the male 
they are peculiarly modified. What numerical relations 
do you find between somites and appendages in the abdo- 
men? (Savigny's law). 

Examine the lower surface of the cephalothorax and 
see if you can find traces of somites, especially in the 
region near the abdomen. How many appendages on 
one of these somites? How many pairs of large legs, 
including the 'pincers' (chelce), do you find? In the hinder 
pair of legs how many joints do you find? Can you 
distinguish exopod and endopod? Compare this leg, 
joint by joint, with the big claw. What change would 
make it into a chela? How many of these legs are chelate? 
Look on the inside of the basal joints of the legs for open- 
ings (outlets of the reproductive organs). If they occur 
on the middle pair the specimen is a female; if on the last 
pair it is a male. What is the sex of your specimen? 

Study the appendages (mouth-parts) in front of the big 
claws. In order to do this properly it will be necessary 
to remove those of one side one by one, by grasping the 
base of the appendage with the forceps and pulling it out. 
Be careful to get all of each appendage, and nothing else. 
The three hindermost (or outer) mouth-parts are the jaw- 
feet (maxillipeds) . Compare the hinder pair with the 
third swimmeret. Do you find basiopod, exopod, and en- 
dopod? Compare it with one of the walking-legs. Which 
part, exopod or endopod, is lacking in the latter? Draw 
each of the maxillipeds. 



CRAYFISH OR LOBSTER. 69 

In front of the maxillipeds come two pairs of accessory 
jaws (maxillae). Remove them carefully and draw. Look 
on the hinder maxilla for a large expansion, the gill- 
bailer (scaphognathite) . Removing these parts exposes the 
mouth, on either side of which is a strong jaw (mandible). 
How do these jaws move in comparison with those of man? 
Take one out and see of how many joints it is composed. 
Draw. 

The cephalothorax is covered above by a large continu- 
ous plate, the carapax. Does this show signs of somites? 
With the forceps lift the hinder corner of the carapax on 
the side where the mouth-parts still remain and see 
where it joins the body. Then with the scissors cut away 
the free portion, thus laying open the gill-chamber and 
exposing the body-wall and the numerous gills or branchiae. 
Are any of these attached to the legs or to the body- 
wall? Move the maxillae and see the operation of the 
gill-bailer. Can water obtain free access to the gills? 
Would the action of the gill-bailer tend to draw water 
over the gills? Remove the gills one by one, noting 
how many there are on each appendage (podobranchiae) ; 
on the joint uniting the appendage to the body (arthro- 
branchiae) and on the side of the body above each append- 
age (pleurobranchice) . 

In front of the mouth occur the ' feelers/ or antennae. 
Could these be compared to the legs? Can you find 
exopod or endopod in them? Examine the basal joint 
of the larger or posterior one (the antenna proper), and 
find an opening, the outlet of the green gland (see below). 
Is it in any way comparable' in position to the reproduc- 
tive opening? In the smaller feelers (antennulae) look 
for the ear-sac on the upper surface of the basal joint. 
(It is covered with a thin membrane, around which hairs 



70 LABORATORY WORK. 

are arranged.) Above the antennulse are the eyes. Are 
they movable? Examine the black portion (cornea), and 
see the small portions (facets) of which it is composed. 

Make a tabular arrangement of the appendages of the 
body,* and ascertain by Savigny's law (p. 68) how many 
somites there are in the body of the crayfish. Compare 
the somites, and see how their diversity is brought about 
by under-development (atrophy) of one part and over- 
development (hypertrophy) of another. (The carapax is 
really but the dorsal portions of the antennal and man- 
dibular somites, the line crossing its middle (the so-called 
cervical suture) being the line of union of these two.) 

Make a side view of the crayfish, twice the natural size, 
naming the parts. 

Internal Structure. 

The dissection should be made under water, the specimen, 
back upwards, being held in position by being pinned to the 
wax bottom of the dissecting-pan, the pins passing through 
the telson and large claws. Open the crayfish along the back 
by cutting away the carapax with the scissors, taking care not 
to injure the underlying parts. Continue the cuts backward, 
removing the upper surface of the abdomen. 

Just beneath the carapax, behind the cervical suture, 
is the oblong whitish heart. How many openings (ostia) 
can you find through its walls? How many tubes (arteries) 
leading from it? With the forceps gently tip the heart to the 
side. Can you find more openings or more arteries? Is 
there a chamber (pericardium) around the heart? Trace 
the arteries as far as you can without injuring other 
parts. 

* For reasons which cannot be discussed here, the eyes, although 
jointed, are not regarded as appendages comparable to the others. 



CRAYFISH OR LOBSTER. 71 

Beneath the heart, and projecting from beneath it in 
front and behind, are the paired reproductive organs. Do 
those of the two sides connect? Can you find the ducts 
leading down from them? Where do they end? Still 
farther in front is the large thin-walled stomach, and on 
either side of this, and reaching back to the heart, is the 
liver, reddish in the crayfish, green in the lobster. Tip 
the stomach backwards and see the oesophagus or tube 
leading to the stomach from the mouth. Tip it forwards 
and find the intestine. Can you find the ducts leading 
from the liver to the intestine? 

Draw the viscera, etc., as far as made out, adding the 
intestine later. 

Cut away heart, liver, reproductive organs, and trace 
the intestine to the vent. Is it the same size throughout? 
Follow the sternal artery from the lower surface of the 
heart downwards towards the floor, taking care not to 
cut anything. 

Take out the stomach, being very careful not to injure 
other structures when cutting the oesophagus. Open the 
stomach and find the teeth; how many? Try to see how 
the teeth grind the food. 

In the front part of the body, close to the antennae, find 
the green glands (paired). Their openings have already 
been found. They are excretory in function (kidneys). 

Cut away the (white) muscles in the abdomen, being 
careful as you approach the floor, and expose the hinder 
part of the central nervous system {ventral cord). How 
are the enlargements (ganglia) arranged with reference to 
the somites of the abdomen? Are the nerves given off 
from the ganglia, or from the cord (ccnnmissure) connecting 
them? Trace the ventral cord forward into the cephalo- 
thorax, carefully breaking away the hard parts which cover 



72 LABORATORY WORK. 

it, and follow it forward to the brain, in front of the mouth. 
How many ganglia do you find in the cephalo thorax? 
Do any show signs of being double? Is the commissural 
cord single or double in this region? Note how the cord 
passes the sternal artery. Is there a ring of the nervous 
system around the oesophagus? Can any of the nervous 
system be said to be above, or any below, the alimentary 
canal? From what part do the nerves to the antennae 
and eyes arise? 

Draw the nervous system from above. 

Beneath the nervous system will be found the ventral 
artery with its anterior and posterior (abdominal) parts. 
Trace the blood-vessels from it to the appendages. Note 
also the blood-vessels in the gills. Sketch a gill showing 
the blood-vessels found. 



SOW-BUG (Oniscus or Porcellio). 

Can you make out three regions in the body: head, 
thorax , and abdomen? Where would you draw the lines 
between the regions? 

Examine a thoracic segment. Does it resemble in any 
way an abdominal segment of a crayfish? Study the legs. 
Can you find exopod and endopod? How many legs 
do you find? Are any of them terminated with pincers? 
Look beneath the thorax for thin overlapping membranes 
attached to the bases of the legs. They will be found only 
in females. Between them and the lower surface of the 
body is a chamber or brood-pouch to contain the eggs or 
young. Do you find anything in this cavity? 

How many segments do you find in the abdomen? 
Notice the last pair of abdominal appendages extending 
behind the body. Turn the animal on its back, and with 
the needle pull apart the flattened plates on the lower sur- 
face of the abdomen. These are the gills. Do they pre- 
sent any of the characteristics of appendages? How 
many of these gills do you find? Examine them all and 
see which ones bear white spots (air-chambers). Draw a 
pair of these gills. 

Examine the head. Where are the eyes? Are they 
on stalks? What are the peculiarities of the antennae? 
Can you, with the lens, find another pair of minute an- 
tennae? The mouth-parts form a short, thick projection 

73 



74 LABORATORY WORK. 

beneath the head. Pick this apart with the needle. How 
many pairs * of mouth-parts can you find? Counting all 
the appendages of the head, how many segments should 
there be in this region? 

Make a tabular statement as for the lobster or crayfish 
(p. 70) and ascertain the number of somites. 

* The two of the hinder pair are united, but should be counted 
as a pair. 



COMPARISONS. 

With one column for Crayfish, the other for Sow-bug, 
give answers to these questions: 

(1) Are head and thorax united? 

(2) Are the eyes on movable stalks? 

(3) How many pairs of walking-feet, counting the 
pincers as such? 

(4) Where are the gills? 

(5) Are both exopods and endopods present? 

Read the accounts of Decapoda (pp. 226 to 229) and 
Tetradecapoda (pp. 229 to 231). 

75 



GRASSHOPPER: LABORATORY WORK. 

Can you distinguish three regions — head, thorax, and 
abdomen — in the body? Where would you draw the lines 
between these regions? and why at these points? 

Notice that the abdomen is made up of a series of rings 
(segments, somites, or metameres) essentially like each other. 
Examine a ring at about the middle of the abdomen and 
see that it is made up of dorsal and ventral hardened halves, 
united by a more flexible membranous portion. Look at 
the side of the somite and find a small opening (spiracle). 
How many somites bear similar spiracles? Has any somite 
more than a pair of spiracles? Could you speak of these 
spiracles as being segmentally arranged f 

Examine the base of the abdomen and see that its first 
somite is incomplete. Look at the lower surface and see 
if you can find the lower half of this ring. On the sides of 
this first ring notice a large oval thin spot (tympanic mem- 
brane), the so-called ear. Can you find a spiracle near 
the ear? 

The tip of the abdomen varies in shape in the two sexes. 
In the female it is provided with two pairs of pointed out- 
growths (ovipositor). The male lacks these, and the tip is 
rounded and frequently upturned. Study this region care- 
fully in each sex, making out the following points: 

In the male notice that the ventral halves of the terminal 
segments are much larger than the dorsal portions. (This 

76 



GRASSHOPPER. 77 

overgrowth is called hypertrophy.) Counting from the 
base, how many rings can you find in the whole abdomen? 
Are any except the first incomplete? Lift the parts on 
the dorsal side of the tip of the abdomen and find the vent. 
On the dorsal side between the vent and the tenth somite 
is a broad plate (supra-anal plate), and on either side of 
this is a small outgrowth from the tenth segment (anal 
cercus). Are these anal cerci movable? Could they be 
regarded as jointed appendages? To which somite do they 
belong? 

In the female study the terminal somites in the same way 
as in the male. Do you find the same dorsal and ventral 
halves? Are any of them hypertrophied? Do you find 
vent and anal cerci? Examine the ovipositor.* Are its 
parts movable? See if they are attached to the eighth and 
ninth segments. 

Draw side and dorsal views of male and female abdo- 
mens, making each sketch at least four inches long. Insert 
all features made out, lettering everything. 

In the thorax recognize three segments , named in order, 
from in front backwards: prothorax, mesothorax, meta- 
thorax, the first overlapping the others dorsally something 
like a cape. How many legs are attached to the pro- 
thorax? Look in the membrane joining the pro- to the 
mesothorax for a spiracle. Study a pro thoracic leg. It 
is made up of a series of joints. Joining the leg to the 
body are two short joints (coxa and trochanter) , then comes 

* As its name implies, the ovipositor is of use in laying the eggs. 
By means of it the grasshopper bores a hole in the earth, and then 
the packets of eggs, passing down through the tube formed by the 
four members of the ovipositor, are deposited in the ground. Other 
allied species use the ovipositor for placing the eggs in leaf-buds 
or in the stems of certain plants. In bees and wasps it becomes 
modified into the sting. 



78 LABORATORY WORK. 

a long femur, next an almost equally long tibia, and lastly 
a several-jointed foot or tarsus. Notice how freely the 
head moves upon the prothorax by means of a flexible 
'neck.' Separate the prothorax from the head and from 
the meso thorax and draw it from the side. 

Study meso- and metathorax together. Notice that on 
the back the line between these somites is very distinct; 
trace this line upon the side, and thence to the ventral 
surface. Do you notice any other lines which seem to 
divide meso- and metathorax? Can you trace them on all 
surfaces? Do you find any spiracles in this region? How 
are the legs related to the somites? Can you recognize in 
each the same parts found in the pro thoracic legs? Where 
are the wings? Are they alike? What is the prevailing 
direction of the ribs or l veins' in them? Can either pair 
be folded like a fan? Is there anything to protect the 
hinder pair when at rest? 

Draw a side view of meso- and metathorax, inserting ex- 
panded wings, legs, etc., and noting especially the spiracles 
and the lines separating the somites. 

Considering the thorax and tip of the abdomen of the 
grasshopper, do you find anywhere a segment bearing 
more than a pair of jointed appendages? * So far as your 
present knowledge goes, would you be justified in saying 
that a pair of jointed appendages indicates a somite of 
the body? (Savigny's law.) 

Notice that the head is made up of a large solid piece 
(epicranium) , to which are attached various movable por- 
tions. On either side of the head is a large compound eye. 
With a sharp knife slice off one of these eyes and examine 
it under a low power of the microscope. Why is it called 

* For reasons which cannot be discussed here, the wings of grass- 
hoppers, etc., are not considered as jointed appendages. 



GRASSHOPPER. 79 

compound? What is the shape of the parts (facets) of 
which it is composed? 

Look on the front of the head for the smaller bead-like 
simple eyes or ocelli. How many of these do you find, and 
how are they arranged? 

On the front of the head, below the eyes, is a broad fold, 
the clypeus, to which is attached a movable upper lip 
(labrum) covering the mouth in front. Near the eyes arise 
two long, slender feelers, or antennce. Could they be re- 
garded as jointed appendages? 

On the lower side of the head is the mouth, surrounded 
by a series of appendages, or mouth-parts. Beginning be- 
hind, remove these one after another with forceps and 
needle. The most posterior is the lower lip, or labium. 
It is in reality double, and consists of the united basal 
joints and, arising from these on either side, a several- 
jointed palpus. Draw the labiumXlO, and then take off 
and draw the pair of appendages, the maxillw, next in front. 
Notice that in these the basal joints are enlarged, one 
forming a sharp cutting-organ, the other a more fleshy 
portion to hold the food in position. The terminal parts 
form a palpus, somewhat similar to the labial palpus. 
Still further in front come the jaws, or mandibles. Move 
these with the forceps. Do they work in the same way 
that your own jaws do? Draw them, and then draw front 
and side views of the head, labelling all the parts. 

Have you found any traces of segments in the head? 
How many pairs of jointed appendages have you found? 
According to Savigny's law, how many segments * must 
there be? 

* Study of the embryos of some insects makes it probable that 
there is one more segment in the head than is shown by Savigny's 
law. 



SO LABORATORY WORK. 



Internal Structure. 



The internal structure of the grasshopper in its larger 
features is readily made out. Select a large female for the 
purpose of dissection; pin it out, back uppermost, in the 
dissecting-pan, in water just deep enough to cover it, and 
with fine scissors cut away the dorsal wall of the abdomen, 
taking great pains to remove nothing but the hard parts. 
In spite of all care the beginner will probably remove the 
heart — a delicate tube lying along the middle of the back — 
with the dorsal wall. Continue the cuts forward, removing 
the dorsal wall of the thorax. Notice the large muscles 
which move the wings. If the specimen has been freshly 
killed, the most striking feature will be a series of silvery- 
appearing air-tubes, trachece, which connect with the 
spiracles and ramify all parts of the body. In alcoholic 
'hoppers' these are distinguishable only with difficulty. 
Between the body-wall and the viscera will be found the 
light-colored fat-body. 

In the anterior part of the abdomen, on either side, is 
a cluster of long oval yellow eggs, and from each mass of 
eggs a delicate tube (oviduct) may be traced backwards to 
the region of the ovipositor. Separate the masses of eggs 
and find, between and below them, the dark-colored ali- 
mentary canal. Follow this forward and back and make 
out in it the following parts: In the hinder half of the 
abdomen the intestine, which in front passes into the much 
larger stomach. At the junction of the stomach and intes- 
tine are a number of fine tubes (Malpighian tubes) which 
are excretory in function. At the anterior end of the 
stomach are a number of larger double-cone shaped tubes, 
the gastric cazca, and in front of these is the large brown 



GRASSHOPPER. 81 

crop. The crop is connected with the mouth by a narrow 
tube, the gullet or oesophagus. Draw the alimentary tract. 

Remove the alimentary canal by cutting through oesoph- 
agus (close to the crop) and intestine, and look upon the 
floor of the abdomen for the nervous system. Can you find 
enlargements (ganglia) in this? How are they arranged 
with regard to the somites? Follow the nervous system 
forward, if possible, into the head. Can you find cords 
passing around the oesophagus as in the crayfish? Is 
there a brain above the gullet? Does the alimentary canal 
pass through the nervous system? Draw the nervous 
system. 

Draw a diagram of a transverse section passing through 
the thorax, showing the body-wall, wings, legs, spiracles, 
egg-masses, nervous cord, alimentary canal, and heart 
in their relative positions. 



COMPARISONS. 

With two columns, one for Grasshopper and the other 
for Crayfish (and Sow-bug) , answer the following questions: 

(1) How many pairs of antennae? 

(2) How does the animal breathe? 

(3) How many segments in the head region? 

(4) How many walking-feet? 

(5) Are there appendages on the abdomen? 

(6) Where are the reproductive openings? 

(7) Are any appendages two-branched? 

(8) Where and what are the excretory organs? 

Read the account of the Hexapoda (pp. 236 to 270) and 
that of the Crustacea (pp. 218 to 231). 

82 



COMPARISONS. 

With two columns, one for Grasshopper, the other for 
Crayfish (and Sow-bug), answer the following questions: 

(1) Is the body made up of a series of segments? 

(2) Do any of the segments have jointed appendages? 

(3) Do you find more than one pair of appendages on 
one segment? 

(4) Are the hard parts (skeleton) external or internal? 

(5) Do the jaws work in a longitudinal or in a transverse 
plane? 

(6) Can the jaws be compared to the other appendages 
of the body? 

(7) Is the heart above or below the alimentary canal? 

(8) Is the brain above or below the oesophagus? 

(9) Where is the largest part of the nervous system? 

(10) How are the two parts of the nervous system con- 
nected? 

(11) Is there any relationship between nerve-enlarge- 
ments (ganglia) and the external segments of the body? 

Read the whole section (pp. 215 to 272) upon the Arthro- 
poda. 

If there be sufficient time the following insects may be studied. 
This will be valuable to the student who is especially interested 
in entomology. 

83 



THE CRICKET. 

Do you find the same regions as in the grasshopper? Are 
there the same number of segments in the abdomen? and in 
the thorax? Are the wings and the feet the same in number in 
the two forms? In the place of the cerci what do you find? 
Could you call these jointed appendages? How many parts 
do you find in the ovipositor of the female? What changes in 
the grasshopper ovipositor would be necessary to make it like 
that of the cricket? Can you split any of the parts of the ovi- 
positor of the cricket? Can you find the ear? 

In the head are there the same eyes, antennae, and mouth- 
parts? Do the mandibles work in the same way? Look on the 
second long joint (tibia) of the foreleg for the ear. Draw all 
the parts mentioned as for the grasshopper. 

84 



< JUNE-BUG' (BEETLE). 

How does the size of the head compare with that of the 
grasshopper? Can you find both ocelli and compound eyes? 
Notice the antennae on the front of the head. Draw one. 
What changes would you need to make in the antenna of a 
grasshopper to make it like that of the June-bug? Can you 
find labrum, mandibles, maxilla, and labium as in the grass- 
hopper? 

How many pairs of walking-legs do you find? Do you find 
segments to correspond? What name must be given to the 
large segment just back of the head? Examine a leg: Do 
you find in it the same segments that occur in the leg of the 
grasshopper? 

Lift one of the hard outer wings (elytra). Do you find 
veins, like those of the grasshopper, in the elytron? Is there a 
second pair of wings? Are they as long as the elytra? How 
are they folded? 

Study the abdomen. Can you find the membranous portion 
uniting dorsal and ventral halves of the somites? Are spiracles 
present? Can you find any 'ears'? How many segments can 
you count in the abdomen? Do you find anal cerci, or ovi- 
positor Separate the flaps at the hinder end of the abdomen. 
Can you find any additional segments? Draw a beetle from 
above with elytra and wings extended. 

85 



DRAGON-FLY. 

Which pair of wings are the larger? What is the general 
arrangement of the veins in the wings? Is the head freely 
movable? What is the size of the compound eyes? How 
many simple eyes do you find? How would you describe the 
antennae? 

Are the mouth-parts fitted for biting? Do they move like 
those of a grasshopper? Do you find upper lip (labrum)? 
maxillse? labium? What is the character of the mandibles? 
Are they toothed? Have any of the mouth-parts palpi? 

Do you find all three of the thoracic segments? Are those 
present of equal size? Are they firmly united to each other? 
What is the relative size of the legs? How many joints in 
the foot? 

How many segments do you find in the abdomen? Are any 
of them partially divided? On what ones do you find spiracles? 
Are there appendages on any of the abdominal segments? 

86 



BEE OR WASP. 

What peculiarities do you find in the antennal joints? Are 
both compound eyes and ocelli present? Are the mandibles, 
like those of the grasshopper, fitted for biting? How do the 
other mouth-parts compare in shape with those of the grass- 
hopper? Do you find a 'tongue'? 

How many thoracic segments? Are all freely movable? 
Which is the smallest? Which bear wings? Whicn pair of 
wings is the larger? Are the veins of the wings many or few? 
Are the wings transparent? 

Does the abdomen join the thorax by its whole width, as 
in the grasshopper? or is there a slender stalk joining the two? 
How many abdominal segments do you find? Squeeze the 
abdomen and look for the sting. Does it compare in any way 
with the ovipositor of other insects? Where was it before 
pressure was applied? 

87 



COMPARISONS. 

Rule a sheet of paper with columns for Grasshopper, Beetle, 
Dragon-fly, and Wasp, and write the answers in each to the 
following questions: 

(1) Are ocelli present? 

(2) Are the antennal joints equal in size? 

(3) Are the maxilla? and labium short and stout, or long and 
slender? 

(4) Are any of the thoracic rings free? 

(5) Which thoracic ring is the largest? 

(6) Which pair of wings is the larger? 

(7) Describe the general structure of the fore wings. 

(8) How many segments in the abdomen? 

(9) Are any appendages besides those of the ovipositor 
present on the abdomen? 

(10) With which column should the cricket be placed? 
Read the sections on Orthoptera (pp. 243 to 246), Hymen- 

optera (pp. 253 to 256), Pseudoneuroptera (pp. 246 to 248), and 
Coleoptera (pp. 250 to 253). 

88 



SQUASH-BUG. 

Can you distinguish three regions in the body? How many 
legs do you find? Have these the same joints as in the grass- 
hopper? How many joints in the tarsus? Do you find com- 
pound eyes, ocelli, and antennae on the head? Examine the 
lower surface of the head and find the beak. See if with needles 
you can separate it in several needle-like parts. This can 
only be done with great care in so small a form as the squash- 
bug. The student, if successful, will find four needle-like 
pieces (mandibles and maxillae) sheathed in a groove-like 
labium. Could this beak be used for biting and chewing, or 
for piercing and sucking? Notice the wings, drawing one of 
each pair. In the anterior wing are the basal and distal parts 
equally thick? How many joints in the abdomen? Where 
are the spiracles? 



BUTTERFLY. 

Notice the relative size of the wings. How are they carried 
when the insect is at rest? Rub the wings and notice your 
fingers. Scrape a wing with a scalpel and study the ' dust ' 
under the microscope. With what is the body covered? Sketch 
the veins in the wings. 

Study the head. Below, notice the proboscis. Straighten 
it out with a needle. At the sides of the base of the proboscis 
see the labial palpi. Are the antennae of the same size through- 
out their length Sketch the head in outline, then remove 
the hairs, etc., which cover it and look for eyes and ocelli, 
inserting what you find in the drawing. 

Do you find in the legs the same joints as in the legs of grass- 
hoppers? Have the tarsi of all the legs the same number of 
joints? Is the base of the abdomen as broad as the thorax? 
Do you find cerci or ovipositor? 

90 



COMPARISONS. 

With columns for Squash-bug and Butterfly, answer the 
following questions: 

(1) What is the relative size of the two pairs of wings? 

(2) How are they carried when at rest? 

(3) Are they naked or covered with scales? 

(4) Are either pair thickened at the base? 

(5) Are distinct labial palpi present? 

(6) Can the proboscis be used as piercing-organ? 

Read the pages referring to the Lepidoptera (pp. 261 to 267) 
and the Hemiptera (pp. 257 to 261). 

91 



LABORATORY WORK: EARTHWORM. 

The student should be supplied with a live earthworm, and 
also with a specimen killed by placing in a dish in which is a 
bit of cloth dampened with chloroform, the whole being covered 
so as to prevent escape of the fumes. After death the worm 
should be pinned out straight and hardened in plenty of 
alcohol. 

Is the body cylindrical throughout? Is it bilaterally 
symmetrical? Can you distinguish between dorsal and 
ventral surfaces? Is the body apparently made up of 
somites? Are they all essentially alike? Draw the worm 
through the fingers; does it move with equal ease in both 
directions? 

Examine the head end for the mouth; is it dorsal or 
ventral in position? Is the ring (preoral lobe) in front of 
the mouth complete? How is it attached to the next 
ring? Examine the surface of the body with a lens for 
bristles (chcetce or setce). Do you find them on each segment? 
How are they arranged on the segment? What was the 
cause of the difference in ease of motion through the 
fingers? Would the chsetse be of value in the motions of 
the worm through the soil? 

Where is the vent? About one fourth the length of 
the body from the anterior end notice that certain rings 
are enlarged and swollen, and that the lines between the 
segments tend to be obliterated. This is the clitellum. 
How many segments are included in it? The clitellum 

92 



EARTHWORM. 93 

is a glandular structure to secrete the cases or cocoons in 
which the eggs are laid. 

Hold a living worm near the anterior end. Does it pro- 
ject a proboscis from the mouth? Look on the back and 
see the red dorsal blood-vessel showing through the skin. 
Study the somites in front of the clitellum, looking for 
openings of the reproductive organs on the ventral surface. 
How many pairs of these do you find, and on what seg- 
ments are they? Leave a dead worm in water for several 
hours; can you separate from it an external transparent 
cuticle? 

Draw a worm from the side, being careful to get in the 
right number of segments, back to the posterior end of 
the clitellum, and bringing out as many of the points dis- 
covered as possible. 

Pin a worm which has been in alcohol with pins pass- 
ing through the preoral lobe and the hinder end of the 
body in a dissec ting-pan. With the scissors open the 
dorsal wall of the body from just behind the clitellum to 
the anterior end, taking care to cut through only the dor- 
sal wall. It is best to make this cut just a little to one 
side of the median line. As you start to lay open the body, 
notice the partitions (septa or dissepiments) running in from 
the body-wall and holding the parts together. Do the 
septa correspond in position to the external rings or to 
the spaces between them? Do they divide up the body 
into a series of body-cavities? Do the cavities of the right 
side correspond in position with those of the left? Is 
there a partition (mesentery) separating the cavities of 
the two sides? 

Cut the septa with the scissors and pin out the body- 
wall. This exposes the digestive tract lying in the axis 
of the body. In it make out the following regions : (1) A 



94 LABORATORY WORK. 

pear-shaped enlargement (pharynx) occupying about half a 
dozen segments in front. Notice the muscle-fibres going 
to the pharynx from the body-wall. (2) A narrower tube 
(oesophagus) leading back through about ten segments 
from the pharynx, and expanding, about segment 16, into 
(3) a heart-shaped crop, which in turn is followed by (4) a 
second enlargement (gizzard) of about the same size. 
(5) From the gizzard the intestine can be traced back to 
the vent. 

Lying above the alimentary tract is the dorsal blood- 
vessel. From it are given off transverse vessels. Are 
these in pairs? Do they correspond to the segments in 
number and position? Are any of them enlarged? In 
what direction do they go? Can you find (by tipping the 
alimentary canal) a ventral blood-vessel beneath? Do any 
vessels connect with it? 

On the top of the anterior end of the oesophagus are 
two pear-shaped bodies, the brain. Can you find nerve- 
cords (commissures) leading downward and backward from 
the brain? 

Arising from either side and extending upwards so as 
to overlap the oesophagus above are lobes of the repro- 
ductive organs. Draw the parts so far made out, viewed 
from above, and then cut through the pharynx and care- 
fully lift up the alimentary canal as far back as the be- 
ginning of the intestine, cutting it off at that point. Now 
sketch the reproductive organs, lifting them up to see if 
other parts occur beneath. 

Examine the cut end of the intestine? Is the inside a 
circular tube? On the dorsal surface of the intestine see 
the dark-green chloragogue organ (a digestive gland, sup- 
posed to be something like liver or pancreas in its action) . 
With what is the intestine filled? 



EARTHWORM. 95 

On the middle line of the floor of the body find the 
ventral nerve-cord, with its numerous enlargements (gan- 
glia). Are these latter equal in number to the somites? 
Do they occur in or between the somites? Trace the 
nervous system forward and find out how it connects 
with the brain. Draw the brain and twenty ganglia of 
the ventral chain connected together. Just outside the 
ventral nervous cord find in each segment (except a few 
anterior) a minute coiled tube (nephridium) . These are 
the excretory organs of the worm, and each opens sepa- 
rately to the exterior between the rows of chsetae. 



COMPARISONS. 

With columns for Vertebrate, Arthropod, and Earth- 
worm, answer the following questions: 

(1) Are paired appendages present? 

(2) Do you find an evident body-cavity? 

(3) Is the alimentary canal supported by a mesentery? 

(4) Is the greater part of the nervous system dorsal or 
ventral in position? 

(5) Is there any segmentation visible from the outside? 

(6) Is there anything which you could call internal 
segmentation? If so, what parts are repeated? 

(7) Is there an external cuticle? 

(8) Does the alimentary canal pass through the nervous 
system? 

(9) Is there an internal skeleton? 

(10) Summing up these points, what two forms do you 
consider to be most similar? 

(11) Draw transverse diagrams of a vertebrate, an 
arthropod, and an earthworm, showing skeleton, body- 
cavity, dorsal vessel, aorta, ventral vessel, heart, kidneys, 
nervous system, appendages, etc., as far as you find them 
in each. Which two seem most alike? 

(12) Can you better bring all three diagrams into har- 
mony by turning any one wrong side up? If so, what one 
must be turned? 

(13) Can you recall any such connection, in any verte- 

96 



COMPARISONS. 97 

brate, between the dorsal and ventral blood-vessels, as you 
find in the earthworm? If so, where and what? 

Read the account, first, of the Annelida (pp. 183 to 189) 
and then that relating to the whole of the Vermes (pp. 178 
to 192). 



THE CLAM. 

For this purpose the student can use either the fresh-water 
clam (Unio, Anodonta, etc.) or the long clam (Mya arenaria) 
of the northern seashore. For the study of the nervous 
system clams which have been a few days in alcohol are better 
than fresh specimens. 

External. 

Notice the shell; of how many parts or valves is it com- 
posed? Are the valves equal in size? They are joined by 
a hinge, dorsal in position, and each valve has a promi- 
nence (umbo) near the hinge. On each valve see the lines 
of growth running parallel with the free margin of the 
shell. Draw a line from the umbo to the free margin of 
the shell, perpendicular to the latter. This divides the 
valve into unequal parts, and of these the smaller is the 
anterior. Now with these facts tell which is the right 
and which the left valve of the shell. Draw one of the 
valves, inserting all points made out. 

Internal. 

Remove the left valve from the clam by inserting a knife 
at either end close to the shell and cutting the muscles 
which lie near the hinge line. Then carefully remove the 
valve, seeing that all fleshy portions are left in the right 

98 



THE CLAM. 99 

valve. If properly done, this will leave the animal covered 
with a thin membrane, the mantle. Projecting through 
this, near the dorsal line, are the adductor muscles which 
keep the shell closed, and which were cut in removing the 
valve. According to their position, these are known as 
the anterior and posterior adductors. Are the edges of the 
mantle thickened? Are the mantles of the right and left 
sides united anywhere along the free margin of the shell? 

Cut through the mantle near its ventral edge and fold 
back. Is it free back to the hinge-line? Cutting through 
the mantle opens the mantle or branchial chamber. In 
this several structures are to be noticed. Arising from the 
side of the body are plaited folds (how many?), the branchiae, 
or gills. Are there branchiae on the right side as well? 
Extending downward between the gills is the soft abdomen, 
terminated at the anterior ventral angle by a more solid 
foot. In front, just ventral to the anterior adductor, are 
two pairs of fleshy flaps, the labial palpi, and where they 
meet at their junction with the body is the mouth. At 
the posterior end of the animal look for two fleshy tubes 
(siphons) formed by the edge of the mantle.* Run a 
wire in each from the outer end and see where it appears 
inside the shell. The ventral siphon is the incurrent or 
branchial siphon; the dorsal is the excurrent or cloacal 
siphon. Draw the parts so far made out. 

Just beneath and behind the hinge is the heart, its 
position in the living animal being readily seen by its 
pulsations. Carefully cut into the chamber (pericardium) 
in which it is situated and make out a central ventricle, 
rather dense in texture, and leading to it on either side a 

* These are small in the fresh-water clams, but are greatly de- 
veloped and form the part commonly but erroneously called the 
'head' in the long clam. 



l.ofC. 



100 LABORATORY WORK. 

delicate tubular auricle * which brings the blood from the 
gills to the ventricle. Notice the intestine passing through 
the ventricle. Just in front of the posterior adductor is 
the dark organ of Bojanus, or kidney. Draw the parts 
made out. 

The alimentary canal and the nervous system are best 
followed in specimens which have been in alcohol a few 
days. In such a specimen insert a probe into the excur- 
rent siphon. Notice that it does not enter the branchial 
chamber. Cut through the thin membrane between the 
gills of the right and left sides, posterior to the abdomen. 
This lays open the cloacal chamber into which the probe 
extends. In the dorsal wall of this chamber, just below 
the posterior adductor, see a pinkish or orange body, the 
parieto-splanchnic ganglion. From this trace backward 
nerves which soon curve forward along the base of the 
gills. Also trace two nerves forward, one on either side of 
the body, until they meet in a pair of cerebral ganglia just 
above the mouth. Are the two cerebral ganglia connected 
directly with each other? From the cerebral ganglia trace 
a pair of nerves downward to the pedal ganglia lying 
between the abdomen and the foot. Sketch the nervous 
system. 

Beginning with the intestine where it leaves the heart, 
trace it posteriorly. On which side of the posterior adduc- 
tor does it pass? Where does it empty? Trace it forward 
from the heart, carefully picking away the surrounding 
tissue with the needles, into and through the abdominal 
mass, and plot the coils which it makes. It will be found 
to pass into a rather large saccular stomach, on either side 

* The auricles are easiest seen in the fresh specimen by carefully 
opening the pericardium and pouring in a little alcohol with a 
pipette. This wiil harden and whiten its walls. 



THE CLAM. 101 

of which is the dark-green liver* Trace the oesophagus 
from the stomach to the mouth. 

Take a clam which has been hardened for a couple of 
weeks in strong alcohol or formol. Cut it transversely in 
slices a quarter of an inch thick, using a sharp scalpel for 
the purpose. Draw the sections and name all the parts 
found. This can be done easily if the previous dissection 
has been intelligently done. 

In the shell which has been removed make out the fol- 
lowing points on the inner surface. Near the dorsal line 
the scars formed by the two adductor muscles, and close to 
the posterior scar smaller scars produced by muscles which 
retract the foot. Following the free margin of the shell 
from the anterior adductor scar, downwards and backwards 
towards the posterior adductor, a pallial line, caused by 
the thickened edge of the mantle. Does this continue 
parallel to the margin all the distance or does it extend 
inwards towards the centre of the shell, forming a large 
bay (pallial sinus)? If the latter be present determine 
what causes it. 

Examine these points in other bivalve shells. Could 
one tell by an examination of the shell whether one or two 
adductors were present, the relative size of the foot, the 
presence of a well-developed siphon, etc.? 

* In a pocket of the stomach in the long clam will be found a 
structure of unknown function, the crystalline style, transparent, 
an inch or more in length. 



THE OYSTER. 

Oysters in the shell should be used. Find the hinge as 
in the clam. Do you find lines of growth? In the same 
way as in the clam distinguish anterior and posterior, right 
and left valves. Is the right or the left valve convex? 

Break the shell at the hinder end and, inserting a knife, 
cut the adductor muscle so as to remove the left valve.* 
How many adductors do you find? Is the mantle edge 
thickened and united as in the clam? Do you find any 
siphons? What other peculiarities do you find in the edge 
of the mantle? 

Remove the mantle from the left side and trace the parts. 
How does the foot compare with that of the clam? How 
do the palpi differ? How many gills? Which adductor — 
anterior or posterior — is absent? Find the heart, just in 
front of the adductor. Lay open the pericardium. How 
many auricles and how many ventricles are present? 
Trace the alimentary canal through the body from the 
mouth to the vent. How is it related to the heart? 

* If you do not know where the adductor is, study a shell already 
removed and find the scar made by it. 

102 



SQUID. 

External Form. 

The head, separated from the body by a 'neck/ bears at 
its anterior end a circle of tentacles; how many? Are 
all of these of equal length? If not, which pair is the 
longer, numbering them from the dorsal surface? On 
the side of the head are the eyes ; behind the eye is a fold 
of the skin, the olfactory organ. The body is surrounded 
with a mantle, bearing at the posterior end a pair of large 
fins. Is the mantle joined to the body all around? If not, 
where is it attached? Projecting from the mantle opening 
is the end of a fleshy tube, the siphon. The side of the 
body on which the siphon occurs is usually called the ven- 
tral side. Can the siphon be compared in structure to 
that of the clam? 

Sketch the squid from the side, showing these points, not 
omitting the color spots (chromatophores) . 

Examine the tentacles more carefully. On their inner 
surfaces see the stalked suckers. Are they similarly ar- 
ranged on all the arms? Examine a sucker with the hand- 
lens, making out the fleshy lip, the horny hooks, and a 
fleshy bottom (piston) in the central cavity. Sketch a 
sucker, considerably enlarged. 

Internal Structure. 

Place the squid in the dissecting-pan, siphon uppermost. 
Cut the mantle longitudinally a little to one side of the 

103 



104 LABORATORY WORK. 

middle, beginning at the free edge and carrying the incision 
to the end of the body. This lays open the mantle chamber. 
Lift the cut edges carefully, looking for the median mantle 
artery running^ from the body to the mantle. Pin out the 
mantle and make out the following points: 

The siphon; notice its inner end; just behind it is the 
end of the intestine. On either side of the siphon are the 
siphonal cartilages, grooved on the surface. Look on the 
edge of the mantle and find a ridge. Close up the mantle 
and see how the parts interlock. 

Behind the siphon, at either side of the body, are the 
gills. What structure have they? Can you see any vessels 
connected with them? Follow the intestine back from 
the vent. Is it free, or is it tied down to the underlying 
structures? Notice that it passes across a dark-colored 
body — the ink-sac. Some distance behind the gills see a 
vessel, the postcava, coming from the side of the mantle 
forward to the body. 

The other features vary considerably accordingly as the 
specimen is male or female. In the female the hinder part 
of the body is occupied with eggs, while upon that part 
between the gills are the large, transversely striated nida- 
mental glands* When these are carefully removed the 
structures are much as in the male. 

On either side of the intestine, a little behind the ink-sac, 
is the small opening of the kidney; the kidneys themselves 
stretch back behind the base of the gills. They are irregu- 
lar in shape. When they are removed f there will be seen 
in the median line the systemic heart. Behind, it gives 
off an arterial trunk, which soon divides to form the median 

* These secrete the capsules in which the masses of eggs are laid. 
f Cut through the thin wall of the kidney just behind the gill, 
pull off the thin skin, and wash away the granular contents. 



SQUID. 105 

mantle artery already noticed, and the lateral mantle 
arteries which follow the postcavse. On either side the 
heart receives a branchial vein, coming from the gill ; while 
in front it gives off an anterior aorta which runs forward. 

Look on the side of the gill nearest the mantle and see 
the branchial artery. Trace it towards the middle line 
and find the branchial heart, just behind the branchial 
vein. This receives the blood from the postcava already 
noticed, and also from a precava which comes from in 
front through the kidney, but is not so easily traced. 
Sketch all parts of the circulatory apparatus which you 
have seen. 

The course of the circulation may be briefly described 
as follows : The blood is forced to all parts of the body by 
the systemic heart. After supplying these regions it 
collects in the pre- and postcavse and is brought to the 
branchial hearts, which pump it through the branchial 
arteries to the gills. From the gills it returns to the 
systemic heart by way of the branchial vein to repeat its 
circuit. 

Carefully trace the intestine backwards from the vent, 
removing the systemic heart and the remains of the kid- 
neys. Just behind the level of the systemic heart it will 
be found to enter the thick-walled, muscular stomach. 
This stomach gives off, behind, a large, thin-walled blind 
sac, which extends far back into the body mass. Close to 
where the intestine leaves the stomach the oesophagus 
enters it. Trace the oesophagus forward to the region of 
the neck, but not farther at present. In its course it can 
be followed through the liver. Sketch the alimentary 
tract as if viewed from the side, inserting intestine, ink- 
sac, stomach, blind sac, liver, and oesophagus, leaving 
room for the anterior end of the latter to be inserted later. 



106 LABORATORY WORK. 

With a single stroke of a sharp scalpel split the head 
longitudinally, making the cut as nearly as possible in the 
median plane. In the section thus made the anterior end 
of the alimentary tract and the central part of the nervous 
system can be easily studied. 

Just inside the mouth, which is placed in the centre of 
the circle of arms, is the oval buccal mass, which is only 
slightly connected with the rest of the head. In this find 
the two horny jaws, black at the tips and shaped some- 
thing like the beak of a parrot. Do these jaws work in a 
vertical or in a horizontal plane? The cavity of the 
mouth lies inside these jaws and passes nearer to the dorsal 
jaw. Just inside the mouth-cavity is a pocket given off 
on the ventral side, in which will be found a horny lingual 
ribbon (radula or odontophore) , covered with minute horny 
teeth. Could this ribbon be used in rasping the food after 
it had passed the jaws ? * Notice that the bulk of the buccal 
mass is made up of muscles arranged to move jaws and 
lingual ribbon. 

From the buccal mass trace the oesophagus backward to 
the point where it was left in the previous dissection. Do 
not cut at first in tracing it, as you would be apt to injure 
other portions. If the section of the head be in the 
median plane, the course of the oesophagus will be easily 
followed without dissection. If not, it can be traced later 
after the nervous structures have been studied. 

A little back of the buccal mass some harder, cartilage- 
like structures will be seen in the cut surface of the head. 
These form a brain capsule, resembling in some respects 
(analogous to) the vertebrate skull. In the* dorsal side 

* This may be mounted as an object for the microscope by 
taking it out, passing it through 95% and absolute alcohols, then 
through turpentine, and mounting it on a slide in balsam. 



SQUID. 107 

of this will be found a large centre, the cerebral ganglion, 
while on the ventral side two somewhat smaller ganglia 
occur. The anterior of these is the pedal ganglion, and 
from it nerves can be traced running into the arms. 
The posterior is the visceral ganglion. The oesophagus 
passes between the cerebral on the one hand and the pedal 
and visceral ganglia on the other. In one half of the head 
demonstrate by dissection that these ganglia are con- 
nected. Except that the ganglia are much closer together 
and the connections correspondingly shortened, are the 
relations the same as in the clam? 

Just ventral to the visceral ganglion is an enlargement 
of the cerebral capsule ; this is the ear. Cut into this and 
notice that it has an irregular cavity. Is there a similar 
structure on the other side of the head? Sketch the 
section of the head, showing the ganglia, jaws, lingual 
ribbon, oesophagus, and ear, in the drawing already made 
of the alimentary tract. 

Split one half of the head in a horizontal plane, having 
the section pass through the middle of the eye. In the 
section thus made study first the eye itself. This is covered 
externally with a transparent cornea, and inside contains 
two chambers, separated from each other by the solid lens. 
The outer chamber in turn is partially divided by a circular 
fold, the iris. The inner chamber is bounded internally 
by the retina, the outer surface of which is marked by a 
thin layer of black pigment. Eehind and dorsal to the eye 
is the optic ganglion, bounded posteriorly by a cartilage 
wall. Trace the connections of the optic and cerebral 
ganglia. Draw a diagrammatic section of the eye. 

Cut into the dorsal region of the mantle from the outside 
and find the horny pen. Continue the cutting so that it 
may be taken out. Sketch it. 



COMPARISONS. 

With two columns, one for Oyster and Clam and one 
for Squid, answer the following questions: 

(1) Is there a distinct head? 

(2) Are there cephalic tentacles? 

(3) Is there a bivalve shell? 

(4) Is the siphon, if present, a part of the mantle? 

(5) Did you find any eyes? 

(6) Are adductor muscles present? 

(7) Is there a bivalve shell? 

(8) Are the gills leaf -like or plume-like? 

(9) Are there jaws? 

(10) Is there a lingual ribbon? 

(11) Are there branchial and systemic hearts? 

(12) Is there an ink-sac? 

Read the accounts of the Acephala (pp. 202 to 208) and 
of the Cephalopoda (pp. 208 to 212). 

108 



COMPARISONS. 

With two columns, as before, for Clam, Oyster, and 
Squid, answer the following questions: 

(1) Is the body bilaterally symmetrical? 

(2) Is there a mantle? 

(3) Are gills present? 

(4) Is there a foot? 

(5) Do you find cerebral, pedal, and visceral ganglia? 

(6) Does the alimentary canal pass through the nervous 
system? 

Read the whole section on the Mollusca (pp. 113 to 
214). 

109 



STARFISH. 

These directions will serve for any species of Asterias. Each 
student should be provided with a specimen preserved in 
alcohol or formol and with at least an arm of a dried specimen, 
as in the dried condition the relations of the plates are more 
easily made out. There should also be available specimens 
with the ambulacral system injected. This is easiest accom- 
plished by cutting off one arm near the disc and injecting 
through the radial canal. 

External. 

The body is shaped like a five-rayed star; in it distin- 
guish the central disc and the arms, or rays. In the centre 
of the disc find the mouth. The side on which it occurs 
is called the oral surface. Projecting from the oral surface 
of each arm are the fleshy tube-feet, or ambulacra, and the 
regions of the oral surface in which they occur are known 
as the ambulacral areas. Sketch this surface in outline, 
showing the parts. 

The surface opposite the mouth is the aboral surface. 
Does it have ambulacra? By feeling and bending see that 
this surface is composed of numerous hard (calcareous) 
plates, and that many of these bear spines. On the 
aboral side of the disc is a rounded body, the madreporite. 
Is it radial or interradial in position; that is, does it lie in 
the line of a ray or between two rays? Sketch the aboral 

110 



STARFISH. Ill 

surface and draw a line through it dividing it into sym- 
metrical halves. How many such lines can be drawn? 
The arm opposite the madreporite is known as the ante- 
rior ray* 

With the needle demonstrate that the calcareous plates 
are not on the outside. What covers them? Are the 
spines movable on the plates? Scattered over the aboral 
surface are numbers of fleshy, finger-like projections, the 
branchice. Look at the very tip of the arm and find the 
rounded red eye-spot (recognized with difficulty in pre- 
served material). 

Internal Structure. 

Cut into the side of one of the arms, carrying the inci- 
sion outward to near the tip, crossing to the opposite side 
and then back towards but not quite to the disc. Fold 
back the flap thus separated and notice the following 
structures : 

Attached to the aboral surface the lobular hepatic co3ca, 
each supported by a thin membrane (mesentery). 

On the floor (oral surface) a series of thin-walled vesicles, 
the ampulla?. By means of a needle ascertain if these am- 
pullae are connected with the ambulacra. 

Continue the removal of the aboral surface from the 
rest of the body, taking care that all soft parts, including 
the hepatic caeca, are separated from it and left in the 
oral portion, that the portion immediately around the 
madreporite be left intact, and that one arm be left 

* The reasons why this is called anterior rather than posterior 
cannot be worked out on the forms selected for dissection, but can 
only be seen by a comparison with the cake-urchins (Clypeas- 
troids) and heart-urchins (Spatangoids) . 



112 LABORATORY WORK. 

untouched. Now find on the aboral surface of each 
hepatic caecum the hepatic duct. Trace these ducts in- 
ward until they enter a saccular structure, the pyloric 
part of the stomach. Do they unite before joining the 
stomach? On the aboral surface of the pylorus is a small 
lobular structure, the branchial tree. How many branches 
has it? Is it radial or interradial in position? Draw a 
line through the starfish passing through the branchial 
tree, dividing the animal into symmetrical halves; how 
does this symmetry compare with that obtained from 
the madreporite? Near the centre of the pylorus is the 
small tubular intestine (frequently torn in removing the 
external wall). It empties by a vent on the centre of 
the disc (difficult to demonstrate in the preserved speci- 
men). Notice the openings into the branchiae. 

Remove the hepatic caeca from one arm and find the 
lobular reproductive organs near the base of the ray. 
Where does this duct connect with the external wall? 
Would you consider this point (at which the duct opens 
to the exterior) as radial or interradial? 

Below (that is, oral to) the pylorus is the cardiac portion 
of the stomach, produced into gastric pouches in each of 
the rays. Trace from these pouches the thin retractor 
muscles into the ray to their attachment to its floor. 

Make a sketch of your dissection, showing in the centre 
the stomach, in one arm the hepatic caeca, in a second the 
reproductive organs, a third the cardiac retractors and 
ampullae, a fourth showing the dorsal surface, and leave 
the other arm for structures to be added later. 

Carefully cut away stomach a little inside the mouth, 
and then trace the stone-canal (a hard S-shaped tube) 
downward from the madreporite to the region around the 
mouth. Examine this circumoral region from the aboral 



STARFISH. 113 

side and find the ten Polian vesicles (much like the am- 
pullae) and, inside of these, the small sacculated racemose 
vesicles. How many are there of these? What do you 
find in the place of the one needed to make symmetry? 
Beside the stone-canal is a thin-walled sac, the so-called 
heart. Sketch the organs in this paragraph and keep the 
drawing for further additions. 

Remove the ampullae, membranes, etc., from the floor of 
one of the rays and see the ambulacral plates which meet 
in the median line. Notice the openings in this ambula- 
cral area by means of which the ampullae connect with the 
ambulacra. Are these ambulacral pores in or between the 
plates? How many rows of them do you find in an arm? 
Sketch these plates in the ray of the drawing left incom- 
plete. 

Turn this same ray over,* remove the ambulacra, and see 
the ambulacral plates from the oral surface. They meet, 
forming an ambulacral groove the edges of which are 
formed by smaller plates (inter umbulacrals) bearing mov- 
able spines. 

Cut off the arm as yet left intact about half an inch from 
the disc and draw the section, including in the sketch the 
ambulacral plates forming the roof of the ambulacral 
groove; outside of these the interambulacrals, and then 
the plates of the aboral surface. Add to these parts the 
branchiae, ambulacra, ampullae, hepatic caeca, and mesen- 
teries in their proper position. 

In the groove of that part of the arm which remains 
attached to the disc notice a tube, the radial canal. Insert 
into this the canula of a hypodermic syringe or other in- 
jecting apparatus, and force in some colored fluid (solu- 

* The points in this and the next paragraph are best made out 
in a dried arm. 



114 LABORATORY WORK. 

tion of carmine or Prussian blue). What happens to 
the ampullse and ambulacra? Part the ambulacra and 
follow the colored radial canal to the region of the mouth, 
and see how this is surrounded by a ring-canal. Are 
stone-canal, racemose vesicles, or Polian vesicles filled 
with the fluid? Insert the radial and ring canals, ampullse, 
and ambulacra in the drawing of the stone-canal, etc. 

Beneath the radial canal is a thickening of the skin, the 
radial nerve, which connects with a circumoral ring-nerve 
just below the ring-canal. 



SEA-URCHIN. 

This will apply to either of the common urchins, Strongy- 
iocentrotus or Arbacia, of the northern Atlantic coast. Each 
student should be provided with an alcoholic specimen and 
with a dried, cleaned, and bleached aboral region of the shell 
(test) of another specimen. For this specimens used in pre- 
vious years may be employed. They are easiest cleaned by 
rubbing off the spines and then bleaching in Eau de Javelle 
or Labarraque's solution (potassium or sodium hypochlorite), 
to be had of druggists. This requires several weeks. A more 
rapid method is to boil the test in very weak potash or soda 
lye, but if the lye be too strong or the boiling too long con- 
tinued the whole will fall to pieces. 

External. 

What is the general shape? Are the spines movable? 
Can you find ambulacra between the spines? In how 
many areas are they arranged? At one pole of the urchin 
find the oral area closed by a thin membrane (peristome) 
and in its centre, teeth (how many?). Do the ambulacra 
radiate from this mouth? If so, where should you look for 
the eye-spot (compare starfish)? 

In a cleaned specimen of the test make out the ambu- 
lacra! areas radiating from the region of the mouth. They 
may be recognized by the presence of the ambulacral pores. 
Do these pores pass through or between the plates? How 
does this condition compare with that found in the star- 

115 



116 LABORATORY WORK. 

fish? Between each two sets of ambulacral plates are 
found the larger interambulacral plates Which plates, 
ambulacral or interambulacral, bear rounded prominences 
for the articulation of the spines? Making a comparison 
with a starfish, where would you draw the line between two 
rays of the sea-urchin? Illustrate by a sketch. 

Follow a ray from the oral area to the pole opposite the 
mouth. Notice in the centre of this pole a circular anal 
area, made up of small anal plates. How many plates 
make up the boundary of this circle? Examine them 
under the lens and decide which one compares in structure 
with the madreporite of the starfish. Is it radial or inter- 
radial in position? How many of these plates bear small 
pores? Sketch this region, showing the anal area and the 
tips of the rays, and label the parts, deciding which of the 
perforated plates must be genital and which must be 
ocular plates by comparing with their relative position, 
radial or interradial, in the starfish. With what is the 
madreporite associated? What parts must belong to the 
aboral surface of the starfish? 

Draw, in outline, a starfish, marking on it the position 
of the madreporite, genital openings, ambulacral and 
interambulacral plates, radial canals, and eye-spots. Cut 
this out and illustrate by bending the rays aborally how 
this starfish can be made to resemble the sea-urchin. 

Internal Structure. 

Open an alcoholic urchin by breaking into the equator 
of the test and then continue the opening by breaking, 
bit by bit, with the forceps around the shell, taking care 
that the fleshy parts beneath be not injured. Continue 
until the whole of the aboral surface is removed, leaving 
all the soft portions in the oral half of the test. 



SEA-URCHIN. 117 

Most prominent at first will be the yellowish reproduc- 
tive organs occupying a position above everything else. 
Are its lobes connected? Can you trace the ducts of this 
organ? Sketch the reproductive system and then remove 
it. This will expose the alimentary canal (brown in color) 
supported by a mesentery. Trace its course, making draw- 
ings as you proceed. How many turns does it make? At 
its oral end the alimentary canal connects with a compli- 
cated apparatus — Aristotle's lantern — composed of numer- 
ous harder portions and muscles to move them. Have the 
teeth any relations to this apparatus? Look on the inside 
of the test for the ampullce, and between them for the 
radial canal. 

Usually in preserved urchins the stone-canal becomes so 
tender as to be easily destroyed. It goes downward from 
the madreporite to the inner end of Aristotle's lantern, 
where it connects with a ring-canal, and from this arise 
the radial canals, in much the same way as in starfishes, the 
whole forming a water-vascular system. As in the star- 
fish, the nervous system follows this water-vascular system. 



COMPARISONS. 

With columns for Starfish and Sea-urchin, answer the 
following questions: 

(1) What is the general shape of the body? 

(2) Are the radial canals inside or outside the hard body- 
wall? 

(3) Do you find branchiae? 

(4) Are all the spines movable? 

(5) Is an Aristotle's lantern present? 

(6) How many divisions to the reproductive organs? 

(7) Are hepatic caeca present? 

(8) Do you find a branchial tree? 

(9) Do you find gastric pouches? 

Read the section on Asteroidea (pp. 276 to 278) and that 
on Echinoidea (pp. 280 to 282). 

118 



COMPARISONS. 

With columns for Sea-urchin and for Starfish, answer 
the following questions: 

(1) Of what is the skeleton composed? 

(2) Are spines present upon the outside of the body? 

(3) Can you speak of the parts as being radiately ar- 
ranged? 

(4) Can you also speak of them as bilateral? 

(5) Do you find in both ampullae and ambulacra? 

(6) Does the nervous system surround the mouth? 

(7) Is there a body-cavity? 

(8) Is there a madreporite and a stone-canal? 

(9) Do you find radial canals? 

Read the whole section on Echinoderma (pp. 273 to 285). 

119 



SEA-ANEMONE. 

The following directions are drawn up for the common 
anemone, Metridium marginatum, of the Atlantic coast. With 
a few allowances they will apply to any form. It requires 
some patience to prepare sea-anemones for laboratory work. 
If merely collected and placed in the preservative fluid, the 
result will be a shapeless mass, in which the student will find 
everything confused. The anemones should be placed in 
shallow dishes of salt water, allowed to expand, and then 
gradually be stupefied by the addition of crystals of sulphate 
of magnesia or sulphate of soda (Glauber's salts), and then, 
when completely stupefied, kill and harden by transferring to 
a 1% solution of chromic acid for three hours. The specimens 
are then washed for half an hour in running water and trans- 
ferred to the preservative fluid — formalin or alcohol. 

External. 

In the prepared specimen notice that the body is cylin- 
drical and may be described as consisting of a column, 
with a base by which the animal was attached, and an 
oral disc bearing a large number of finger-like tentacles, 
in the centre- of which is the mouth. Which tentacles, 
inner or outer, are the larger? If there be an increase in 
number of tentacles during growth, which ones would 
probably be the older? What is the shape of the mouth? 
How many thickened places do you find in the mouth? 
These thickened portions are called siphonoglyphes. Could 

120 



SEA-ANEMONE. 121 

they be used to indicate bilateral symmetry? Make a 
drawing of the animal showing the column, oral disc, etc. 
Cut off a few tentacles and see if they be hollow or solid. 

Internal Structure. 

Cut the animal with a sharp knife into two portions, 
the incision being made parallel to the oral disc and pass- 
ing through the body about a quarter of an inch from the 
oral end. In the upper portion (i.e., that nearest the oral 
disc) will be found an oesophagus extending inwards from 
the mouth. Can you trace the siphonoglyphes into this 
tube? Extending inwards from the outer wall to the 
oesophagus are six * pairs of partitions, the primary mesen- 
teries or septa. The result of this is that the space inside 
of the body is divided into a series of chambers. The 
chambers between the septa of a pair are called the intra- 
radial, those between the pairs of septa the interradial, 
chambers. The interradial chambers will be found to be 
partially subdivided by other pairs of septa (secondary, 
tertiary, etc.) which extend outwards from the body- wall, 
but which do not reach the oesophagus. 

Examine the primary septa and find on each a muscle 
extending in the direction from oral disc to base. Are 
these muscles on the inter- or intraradial sides of the septa? 
Examine all the primary septa before deciding this ques- 
tion. Then sketch the cut surface, inserting body-wall, 
oesophagus, and primary septa; and on each of the septa 
put the muscles on the proper surface. If this be done, it 
will be found that there is but one plane which will divide 

* Frequently variations will be found in the number and arrange- 
ment of the septa; these exceptional forms should be compared 
with the more normal specimens. 



122 LABORATORY WORK. 

the animal into exactly symmetrical halves. The septa 
through which this plane passes are the directives. Do 
they correspond in position to the siphonoglyphes? Study 
a few of the incomplete septa. Have these muscles like 
the others? At the oral ends of the septa look for open- 
ings (septal ostia) through these partitions. 

Split the other part of the animal lengthwise and pin 
out under water. Notice that the oesophagus does not 
reach the base. Could food pass from the oesophagus into 
the inter- and intraradial chambers? Do you find any 
body-cavity distinct from the digestive cavity? Do you 
find any opening to compare with a vent? 

Along the free edges of the mesenteries are the coiled 
mesenterial filaments. Do they present the same appear- 
ance nearer the oral disc that they do farther down? On 
the sides of the septa near the mesenterial filaments are 
the reproductive organs (not always plainly visible). 



A HYDROID (Pennaria). 

For this purpose it is well to have some alcoholic material, 
and also some mounted slides, which can be used, year after 
year, with successive classes. To make these mounts the 
alcoholic material should be washed for half an hour in water 
and then stained for twenty-four hours in alum cochineal or 
for an hour in borax carmine. 

After staining, the specimens should be placed in 80%, 95%, 
and absolute alcohol for at least two hours each, and then 
left the same length of time in oil of clove. The best specimens 
may then be selected, placed upon the microscope-slides, the 
oil drained off, and a drop or two of Canada balsam added, and 
a bit of thin glass (cover-glass) placed on the specimen. The 
slides should be allowed to become dry and hard (which will 
take some weeks) before being placed in the hands of the 
student. It must be borne in mind that all of the above 
details are necessary; omissions will result in failure. 

Examine a colony under the hand-lens or low power of 
the microscope, and notice the branching stem (hydro- 
caulus) bearing on their tips the fleshy hydranths, or 
zooids. The hydrocaulus is covered with a horny, tube- 
like perisarc. Does this present any striking peculiarities? 
Sketch the whole colony, making the hydranths half an 
inch in length. 

In a single hydranth see that there is a balloon-shaped 
body, the neck of the balloon being the proboscis, at the 
end of which is the mouth. The hydranth is covered with 

123 



124 LABORATORY WORK. 

tentacles. Is there any regularity in their arrangement? 
Are they all similar? Look on various hydranths for 
globular outgrowths, medusa-buds. Sketch a hydranth 
enlarged, showing the points made out. 

Study a mounted specimen under higher microscopic 
powers, and see that the zooids are made up of two layers 
and that they contain a central digestive cavity. Can you 
trace the layers and the cavity into the hydrocaulus? 
Could food taken into one of the hydranths pass to another 
hydranth? Are the tentacles solid or hollow? Examine 
the tip of a tentacle of the series nearest the mouth, and 
see the large oval nettle-cells imbedded in it. (In favor- 
able specimens threads can be seen extending from the net- 
tle-cells.) Sketch a hydranth enlarged, showing layers, 
digestive tract, etc., and a medusa-bud. 

Look carefully over the hydranths and see if you can find 
any traces of an oesophagus turned into the body as in the 
sea-anemone; of septa, and of mesenterial filaments. Do 
any individuals show a bilateral nature? 



A HYDROID (Clava). 

Clava is common along the whole New England coast, form- 
ing small salmon-colored clusters on the rockweed (Fucus) 
near low-water mark. The specimens should be collected and 
allowed to expand in salt water. They are then killed with a 
saturated solution of corrosive sublimate and passed through 
successive strengths of alcohol, being finally preserved in 85% 
Great pains must be taken to remove every particle of the 
rockweed from the specimens or they will soon be so altered 
as to refuse to stain. Each student should have a colony. 
for study and also a slide of stained sections, cut parallel to 
the long axis of the hydranth. These slides may be used year 
after year. 

Examine a colony under the hand-lens, noting that it 
is composed of hydranths, united at the base by a delicate 
network (hydrorhiza) . Do you find any perisarc (p. 123)? 
What is the shape of the hydranth? Are the tentacles 
arranged with any regularity? Where are the medusa- 
buds ? Draw. 

In a mounted and stained slide of longitudinal sections 
hunt with the compound microscope for a section passing 
through the mouth. Make out the central digestive 
cavity and in its walls see two distinct layers, an outer 
ectoderm and an inner entoderm. Trace ectoderm and 
entoderm to the oral end. After passing the mouth with 
which layer does the food come in contact? Find a sec- 

125 



126 LABORATORY WORK. 

tion through the base of a tentacle; is the tentacle hollow? 
Can you trace both layers into the tentacle? Draw the 
section. Trace the layers into a medusoid bud. Between 
the layers in the bud are the reproductive products. 
In a male specimen these will appear as a multitude of 
dots (spermatozoa) ; in a female there will be a single egg 
in each bud. In the egg make out the large mass (proto- 
plasm) with near its centre a spherical mass (stained), 
the nucleus. In the nucleus there will usually be seen a 
deeply stained body, the nucleolus. Add a medusa-bud to 
the last drawing. 

Read in this connection pages 154 to 156 upon the body 
layers, and pages 140 to 142 upon the cell. Do the eggs 
agree with the account of a cell? Examine both ecto- 
derm and entoderm with the high power. Can you dis- 
tinguish cells in either? Draw a bit of the wall greatly 
enlarged showing the structure oi both layers and bring- 
ing out a thin structureless layer (the supporting layer, or 
mesoglcea) between the two. 



A HYDROID MEDUSA. 

For this purpose the form Gonionemus, common at Wood's 
Hole, is most available; in default other bell-shaped forms 
may be used. As there is no dissection to be done, the speci- 
mens may be used year after year, if care be taken that they 
be not injured. 

Notice that the body is somewhat umbrella-shaped, 
and that you can distinguish a convex or exumbrella 
from a concave or subumbrella surface. From the centre 
of the subumbrella projects a proboscis or manubrium 
comparable to the handle of the umbrella and bearing 
the mouth at its extremity. What is the shape of the 
mouth? 

Trace the digestive or gastral cavity from the mouth 
through the proboscis to the centre of the umbrella and 
thence note the four (more in some species) of radial 
canals extending out to the margin of the disc, where they 
empty into a ring-canal. Notice the tentacles attached to 
the margin of the umbrella. Are they the same in num- 
ber in each quadrant? Are any of them opposite a radial 
canal? Find the reproductive organs on the radial canals. 
Sketch the medusa from the exumbrellar side. 

Examine it now from the subumbrellar surface and note 
that the opening of the umbrella is contracted by a thin 
membrane, the velum, with an opening in the centre. 
Make a diagrammatic section of a medusa showing manu- 
brium, radial and ring canals, tentacles and velum. 

127 



COMPARISONS. 

With columns for Sea-anemone and for Hydroid, answer 
the following questions: 

(1) Are the animals simple or do they form colonies 
connected together? 

(2) Can you find traces of bilaterality in the animals? 

(3) Are septa present? Is the digestive cavity simple, 
or is it subdivided into chambers? 

(4) Is there an in turned oesophagus? 

(5) Are the tentacles hollow or solid? 

Read the accounts of the Hydrozoa (pp. 165 to 169) 
and of the Scyphozoa (pp. 169 to 174). 

128 



COMPARISONS. 

Answer the following questions for Sea-anemone and for 
Hy droid : 

(1) Has either a radial arrangement of parts? 

(2) Are tentacles present? 

(3) Is there a body-cavity apart from the digestive 
cavity? 

(4) How many openings to the digestive tract? 
Read the section on Ccelenterata (pages 162 to 177). 

129 



SPONGES. 

A. — A Calcareous Sponge (Grantia). 

Notice the shape. Is the surface smooth? How many 
openings do you find? What differences do you find 
between the ends? Split the sponge lengthwise with a 
sharp scalped laying open the central cavity (cloaca). 
Where is the large opening (ostium) by means of which the 
cloaca is connected with the exterior? By what is it sur- 
rounded? In the walls of the cloaca notice the openings 
(excurrent canals) — best seen after the sponge has dried. 
In the cut walls see the small chambers (ampullce). Draw 
one half of the sponge, naming the parts. Cut the other 
half of the sponge transversely and notice the radially 
arranged ampullae. Place a bit of the sponge in weak 
hydrochloric acid. What occurs? Boil another bit in 
caustic potash (a few drops of a 5% solution), then place 
the fluid on a slide ; examine under the microscope. Draw 
the spicules which you see. Crush a dry bit of the sponge 
in the fingers. Has it any elasticity? 

B. — A Bath Sponge (Spongia). 

Select small rounded sponges for this purpose. Notice 
the irregularity of the surface. Do you find any large open- 
ing in any way comparable to the ostium of the calcareous 
sponge? If so, split the sponge through this opening and 

130 



SPONGES. 131 

study the section. Can you find canals branching from the 
ostium? If so, sketch their arrangement. 

Crush a bit of the dry sponge between the fingers. How 
does it compare with the other form? Examine a very thin 
bit of it under the microscope; can you find spicules? 

It is to be noted that in the bath sponge of commerce 
only the hard or skeletal parts are present, the flesh having 
been washed away. In the calcareous sponge, as put up 
for laboratory use, flesh and skeleton are both present. 

Read the section on sponges (pp. 158 to 161). 



AMCEBA. 

Dr. H. S. Jennings has described a method of cultivating 
Amoebce and other Protozoa for class work. Glass dishes about 
3 inches deep and 8 or 9 inches in diameter are crowded full 
of various water plants, especially Ceratophyllum, Elodea, etc., 
and are then filled with water and allowed to decay. Several 
such dishes should be prepared so that a supply will be certain. 
After a certain time (say about two weeks) the layers of plants 
at the surface of the water will be covered with a brown slime. 
Some of this should be scraped from the plant, placed on a 
slide and examined under the microscope. As frequently the 
Amoebce in a culture last but two or three days, several cultures 
made at different dates should be on hand. These cultures 
will also afford other Protozoa such as Arcella, Difflugia, Stentor, 
Paramcecium, etc. 

The slide with the slime known to contain Amoebce is 
covered with a thin cover-glass and examined under a 
rather high objective (-§- inch: Leitz No. 5, Zeiss C). When 
Amoeba is found note the following points: A central 
body from which radiate slender prolongations (pseudo- 
podia). Are the pseudopodia regularly arranged around 
the body or are they more numerous on one side? Are 
they simple or branched? 

In the body make out a granular internal portion, the 
endosarc, covered by a clearer external layer, the ectosarc. 
Do both layers enter into the pseudopodia? Watch 

132 



AMCEBA. 133 

the endosarc closely and see if the granules change their 
relative position. In the endosarc make out food vacuoles 
containing substances (differing in color) which have been 
taken in as food. Frequently the food particles are sur- 
rounded by a space filled with a clear fluid. Also make 
out, if possible, the contractile vacuole, clear and pale pink 
in color, which quickly contracts and more slowly reforms 
itself. Time the contractions. 

Watch the animal as it moves on the slide. Make out 
the way in which it travels. Draw the animal in outline 
when moving, at two-minute intervals. Jar the slide. 
Does the animal respond, and if so, how? 

Place a drop of 1% acetic acid at one side of the cover- 
glass and a bit of blotting- or filter-paper at the other, 
thus drawing the acid under the cover and over the amoeba. 
What changes take place in the animal? Notice that 
this brings out a somewhat spherical body, the nucleus, 
in the interior. Examine other living specimens and see 
if you can recognize the nucleus in them. Draw an 
Amoeba, inserting all the features you have made out, 
labelling all the parts. 



PARAMECIUM. 

Paramcecium, as well as other ciliate protozoans, may be 
obtained in the cultures prepared for obtaining Amoeba. They 
may also be found in water in which hay has been allowed to 
stand for about two weeks. These cultures should therefore 
be prepared some time before the laboratory work upon them. 
It is well, a day before use, to place some carmine powder in the 
water. 

Take a drop or two of water on a slide, cover with a 
cover-glass, and examine with a low power of the micro- 
scope. If Paramcecia be present they will be seen as 
small bodies swimming rapidly through the water. 
Examine more carefully under a higher power and make 
out the following points: 

The body is covered with innumerable fine hairs (cilia) 
which are in constant motion. Are the cilia on all parts 
of equal size? Does one end of the animal usually go 
in front? On one side of the body is an opening (cytostome) 
leading into the body. How are the cilia arranged with 
reference to this? Follow the tube (cytopharynx) inward 
from the cytostome. Where does it end? Is it ciliated 
internally? In the protoplasm of the body can you dis- 
tinguish ectosarc and endosarc (see p. 132)? Do you find 
a contractile vacuole (p. 133) or more than one? What is 
its shape at fullest extent (diastole) and at contraction 
(systole)? Draw weak acetic acid under the cover-glass. 

134 



PARAMECIUM. 135 

This will bring out the nucleus. Where is it situated? 
and what is its shape? Draw a Paramcecium, inserting 
and naming all parts made out. 

Allow another drop of water containing Paramcecia to 
dry, watching the process under the microscope. As the 
animal begins to dry note that it renders distinct a cuticle 
covering the surface. Also note the way in which the 
cilia are connected with the sub-cuticular protoplasm. 
Sketch the appearance presented. 



COMPARISONS. 

With columns headed respectively Amoeba and Para- 
modcium answer the following questions: 

(1) Does the body undergo marked changes of shape? 

(2) Can you distinguish permanent regions? 

(3) Are the processes from the general body-surface 
temporary or permanent? 

(4) Are ectosarc and entosarc distinguishable? 

(5) Is there any definite place for taking food? 

(6) Is there a cuticle? 

(7) Is there a contractile vacuole? 

(8) Can you find a nucleus? or more than one? 

(9) If a cell be defined as a mass of protoplasm with a 
nucleus, are these forms unicellular or multicellular? 

Read the section on the Protozoa (pp. 144 to 153). 

136 



THE ANIMAL KINGDOM. 

At first sight animals and plants seem entirely distinct. 
We say that animals move, have sensation, have organs of 
feeding, of respiration, motion, etc., and that the plants 
lack all these. When we contrast a cat and a cabbage 
these and many other points of difference are at once 
forced upon us, while the features in which they resemble 
one another seem to be extremely few. If, however, we 
carry our comparisons farther and take the lower forms 
into account, we soon find that these distinctions fail. We 
find many animals* which are as firmly fixed as any 
tree, while we find many undoubted plants which move 
through the water as freely as any fish. We find, again, 
many plants which have evident powers of sensation. 
House-plants in a window turn their leaves towards the 
source of light; the leaves of the sensitive-plant droop if 
they be touched; while the reproductive elements (zoo- 
spores) of many low aquatic plants will recognize the 
presence of and swim towards a trace of mafic acid. On 
the other hand, sensory organs are as poorly developed 
in sponges, and in many Protozoa, as in most plants. 

* Frequently the term animal is restricted to members of the 
group of mammals. Thus we hear one say 'animals and birds.' 
This is not correct. A bird, a fish, or a clam is as truly an animal 
as is a cat. 

137 



138 SYSTEMATIC ZOOLOGY 

Plants really have their organs of feeding and of respi- 
ration in their roots and leaves, while animals as high as 
the parasitic worms have no special organs for taking food 
or for respiration, the absorption of nourishment taking 
place by the whole surface of the body. 

Several other tests have been suggested to separate 
animals from plants. Plants reproduce by seeds, by 
spores, and by buds; animals by means of eggs. Plants 
take up carbon dioxide and give off oxygen; animals use 
oxygen and give off carbon dioxide. Plants take either 
liquid or gaseous nourishment, while animals partake of 
solid food. Plants may have a peculiar green coloring 
substance called chlorophyl, lacking in animals. Plants 
produce a peculiar chemical substance known as cellulose. 
These features when accurately analyzed are all seen to 
have their exceptions. Many animals reproduce by bud- 
ding, while the sexual reproduction of animals and of 
plants is essentially the same. Plants require oxygen as 
much as animals, and it is only the green plants which 
give off oxygen; a mushroom or a toadstool takes up 
oxygen and gives off carbon dioxide the same as does 
any animal. Quite a number of animals possess chloro- 
phyl, while it is lacking from many plants; and cellulose 
is found even in the Tunic a ta. In the matter of food 
the distinction is a little sharper. While some animals 
like the parasitic worms take only nourishment in solution, 
no plant takes solid nourishment. 

Yet, although we cannot frame a perfect definition which 
will at once separate all animals from all plants, we prac- 
tically have little difficulty in deciding any case that is 
likely to arise in our every-day experience as tt> whether 
the form in question shall be placed in the one kingdom 
or in the other. 



THE ANIMAL KINGDOM. 139 

The difficulty of framing a definition arises from the 
fact that both animals and plants are members of the liv- 
ing world, and hence have many features in common, 
which may be summarized in the expression that they 
are alive. We do not know what life * is ; we only know 
it by the phenomena which it exhibits, which may be 
briefly stated as follows: 

All living beings are composed of a peculiar substance 
(or group of substances) called protoplasm, and this proto- 
plasm is known only as the product of life. When un- 
mixed with other substances it is semifluid, transparent, 
and slightly heavier than water. It consists of a large 
number of chemical elements — carbon, oxygen, hydrogen, 
nitrogen, sulphur, and phosphorus predominating — but 
how these are arranged is as yet one of the mysteries. 
When treated with the reagents of the chemist it dies 
and is no longer protoplasm. 

Protoplasm, and consequently the animals and plants 
which contain it, exhibits certain properties. It can take 
non-living substances and convert them into a part of itself, 
that is, make them alive. The bread and the roast-beef 
which we eat are dead; yet we know that they become 
parts of ourselves, not in the shape of bread and roast-beef, 
but as our own protoplasm. This process is known as 
assimilation, and continued assimilation results in growth. 
A snowball grows by accretions on the outside, but the 
growth of animals and plants occurs all through the body 
and throughout every part of it. It is a growth of the 
protoplasm. 

* Frequently the expression 'vital force' is used, as if there were 
some distinct force in nature exhibiting itself only in living forms. 
This is entirely unnecessary, for each and every phenomenon of life 
can be explained by physical and chemical means. 



140 , SYSTEMATIC ZOOLOGY. 

Protoplasm has the power of spontaneous motion. 
Under favorable conditions we can see its particles chang- 
ing their relative position, or we may see the mass move as 
a whole. It moves also in response to external influences, 
or, as the physiologist expresses it, it reacts to stimuli. 
Thus some protoplasm will turn to light, other kinds will 
try to avoid it. Heat, up to a certain degree, will increase 
its action, while electricity will cause it to contract. 

Protoplasm has the power of reproduction, by which we 
mean that portions can separate from the parent mass and 
can then carry on all the processes which could be per- 
formed before the separation took place. 

These and a number of other features not so easily de- 
scribed are characteristic of protoplasm, and they occur in 
no non-living substance. They are, too, the phenomena 
of life, and hence protoplasm has been aptly termed the 
physical basis of life. 

THE CELL. 

In most animals and plants the protoplasm is not a 
continuous mass, but is divided into small particles called 
cells, which, since they are the elements of which the 
organism is composed, are the morphological units of 
structure. It is almost self-evident then that in order 
clearly to understand either the structure or the various 
phenomena of either animal or plant we must have a 
knowledge of the cell. Hence it is that within recent 
years the study of the cell — cytology — has attained great 
prominence. 

A cell may be defined as an individual particle of proto- 
plasm with a specialized portion, the nucleus, in its in- 
terior (fig. 1). Nucleus and protoplasm differ in many re- 



THE CELL. 141 

spects. The nucleus has a different refractive index, so 
that it stands out, under the microscope, like a drop 
of oil in water. It has a great amnity for certain 
stains, and hence in microscopical 
preparations it is brightly col- 
ored, while the protoplasm is J$?C 
usually but slightly stained. 
Physiological experiments show $£%& . 
that the nucleus controls the 




action of the cell 
is all but conclusive 
it includes the 
heredity. 

In a few minute forms, both ani- 
mals (Protozoa) and plants, the FlG 1 ._ Diagram of a ceU . c , 
whole organism consists of but a ^ y ° c XZ 3SS? ££S£? 
single cell, which consequently 

carries on all the functions of life, but all the rest are 
multicellular. In the multicellular animals (Metazoa) the 
cells are not all alike, but may be divided into groups or 
layers specialized in different directions. This differentia- 
tion is both of form and of function. The cells of the 
separate layers differ in shape and have different work to 
perform, there being what is termed a division of labor 
among the groups of cells. 

All animals above the Protozoa reproduce by eggs. 
These eggs, when carefully studied, are found to agree in 
their essential characteristics. Each, in fact, is a cell 
(p. 126) containing a nucleus; but to these essentials 
other structures — shell, white, yolk, etc. — may be added. 
Each egg, under proper conditions, is capable of growing 
into a form like that which produced it. The essential 
condition is that a peculiarly modified cell, the spermato- 



H2 SYSTEMATIC ZOOLOGY. 

zoan, unites with the egg, and then the compound cell is 
capable of development.* Reduced' to its simplest terms, 
the process of development may be briefly stated thus: 

After union with the sperm-cell (fertilization) the egg 
divides again and again, the result being the formation 
of a large number of cells, all connected together, which 
later arrange themselves in layers (p. 154) and then 
develop into organs. This type of reproduction is known 
as sexual reproduction, since egg-cell and sperm-cell are 
produced by animals of different sexes. 

In many Protozoa something similar occurs. Here we 
find a union of different individuals, and as each protozoan 
is a single cell, this union of individuals is comparable, to 
a certain extent, to the union of egg-cell and sperm-cell. 
With most Protozoa, however, after this union (conjuga- 
tion) the individuals separate and each divides, thus pro- 
ducing new individuals (cells), which differ from the cells 
produced by the division of the eggs in that they never 
arrange themselves into layers, but each forms a dis- 
tinct individual like the parent. 

CLASSIFICATION. 

In order to show the relationships of the various forms 
of organized life resort is had to classification in which 
forms very near each other are grouped together, and 
these groups in turn are similarly united, and so on until 
the whole living world is included in the largest group. 
The process and the principles involved can best be illus- 
trated by a concrete case. 

* In a few cases, as in the honey-bee, the eggs can normally 
develop without union with a spermatozoan. This is called par- 
thenogenesis. 



CLASSIFICATION. 143 

The lion, tiger, leopard, puma, common cat, etc., differ 
among themselves by minor characters, as color, size, 
etc., and hence each is regarded as a distinct species. 
On the other hand they all show marked resemblances 
in number and character of teeth, and in possessing claws 
which can be retracted into sheaths. Hence all these and 
similar forms are united into a group or genus of cats. 
So, too, the dog, wolves, foxes, etc., can be grouped into 
a genus of dogs. Again cats and dogs exhibit resem- 
blances in that they walk on the tips of the toes — are 
digitigrade — while bears and raccoons walk on the sole 
of the foot — are plantigrade. Bears, cats, and dogs are 
all flesh-eaters, and correlated with this have peculiarities 
of structure which leads to their being united in a higher 
group or order of carnivores. In turn carnivores, ele- 
phants, horses, rats, whales, and man are grouped as a 
class of mammals, the points of union being that they 
nourish the young by milk, have bodies more or less 
covered by hair, etc. For these and other grades of 
similarity the following terms are used, the higher coming 
first, the minor last. 

Kingdom 
Phylum 
Class 
Order 
Family 
Genus 
Species 

Individual. 

Besides, other intermediate divisions, as superorders, 
subfamilies, etc., can be interpolated in the series. 

In speaking of an animal (or a plant) two names are 



144 SYSTEMATIC ZOOLOGY. 

used, the generic and the specific. Thus the cats all 
belong to the genus Felis, and we have correspondingly 
Felis leo, F. tigris, F. pardalis, F. domesticus, etc., for the 
forms enumerated above. The specific name may be used 
again and again in different genera, but the generic name 
can be used but once in the animal kingdom. This use 
of generic and specific names was introduced by Linne, 
and was his greatest contribution to science. It must be 
remembered, however, that these names are but aids in 
the bookkeeping of zoological science. 

Animals may be classified in various ways, but that 
universally adopted is based upon structure. Hence the 
study of anatomy is all important as a foundation for 
this work. It therefore becomes necessary to distinguish 
between two kinds of resemblance, that of analogy and 
that of homology. Analogy is a resemblance in function 
and not necessarily in structure; homology is based on 
structure without necessarily similarity in function. Thus 
the wings of a bird and of a butterfly are analogous in 
that both are organs of flight, but they are totally different 
in structure. The wing of a bird and the arm of man 
are homologous, since the structure is essentially the same 
in each, .while their functions are different. The wing of 
a bat and that of a bird are both analogous and homol- 
ogous. 

Phylum I.— PROTOZOA. 

The animal kingdom is divided into two great groups, 
the Metazoa, in which the body is made up of many cells, 
and the Protozoa, which may be defined as animals each 
consisting of a single cell. A little thought will show that 
this difference is in reality very great. In the Metazoa 



PROTOZOA. 145 

certain groups of cells become adapted (specialized) for the 
performance of certain work in the body, and the more 
specialized they become the more restricted are they in 
their lines of work. Thus in man the cartilage and bone- 
cells are solely for the support of the body, muscle-cells for 
the moving of parts or of the body as a whole. When, 
however, we turn to the Protozoa, composed of but a 
single cell, we find that this one cell has to do all the work 
which in the Metazoa is shared by the several groups of 
cells. It has to feed, to move, to excrete waste matters, 
and to reproduce its kind. In a word, the cells of the 
Metazoa are differentiated in various directions; those of 
the Protozoa are undifferentiated. 

The Protozoa show great variety in shape, appearance, 
and habits. In some there is no differentiation between 
the different regions of the cell which composes the body, 
excepting the fact that a nucleus is usually (if not always) 
present. Food may be taken in at any point ; any portion 
may be used for locomotion ; and indigestible portions may 
pass out anywhere on the surface. By feeding they grow, 
and when growth reaches a certain limit the animal (cell) 
divides, and we have now two individuals in the place of the 
original one. 

In other Protozoa different regions in the cell may be 
specialized in different directions and give rise to what 
may be called cell-organs. A single example must suffice. 
In the form figured (fig. 2) we have but a single cell, 
but it is a cell of definite shape. Externally the body is 
covered with a denser layer, comparable in position and 
use to a skin. A little deeper are developed longitudinal 
lines of contractile material which act in the same way as 
the muscles of the Metazoa, moving one part on another. 
Over the outer surface are minute hair-like organs (cilia) 



146 



SYSTEMATIC ZOOLOGY. 



which are in constant motion, and when the animal 
casts itself loose these serve like 
so many oars to propel it through 
the water. At the larger end of 
the body these hair-like organs 
become much larger, and they 
are here arranged in a spiral. 
The effect of their constant mo- 
tion is to create a minute whirl- 
pool in the water, the centre of 
which is in an opening in the 
larger end. This may be com- 
pared to a mouth. The water 
brings with it minute particles 
suitable for food, and these pass 
through the mouth into a cavity 
comparable to a gullet, from which 
they pass into the central part of 
the cell, where they are digested. 
Then the indigestible portions are 
at last passed out from the body 
at a fixed point, the functional 
vent. The large cilia always 
move in a regular and rhythmic 
manner — a fact which would im- 
ply that they were connected and 
controlled in some manner in their 
action; and high microscopic powers show at their bases 
a cord of somewhat denser material which takes the place 
of a central nervous system. If this be cut, the cilia no 
longer work in harmony. Finally, all animals, in doing 
work, produce nitrogenous waste, which must be got rid 
of by means of kidneys. In the form figured the kidneys 




Fig 



2. — Diagram of a Proto- 
zoan based upon Stentor. 
c, large cilia around the oral 
disc; cv, contractile vacuole; 
g, gullet ; m, mouth; mu, mus- 
cular bands ; n, nucleus ; nr, 
nerve-ring. 



PROTOZOA. 147 

are represented by a space on the interior {contractile vacu- 
ole) which regularly enlarges and contracts, and at each 
contraction this waste is forced out into the surround- 
ing water. All of this is in a single cell. 

Occasionally there occur compound Protozoa in which 
several, or even hundreds, of cells (animals) may be united 
in a 'colony/ but even in these cases the essential fea- 
tures persist. There is no differentiation among the cells, 
each being like all the rest and each for itself carrying 
on all the functions of life. 

The Protozoa, of which many thousand different kinds 
have been described, are very minute, only a few being 
visible without a microscope. The great majority of 
them are aquatic, and they are abundant in stagnant 
water, especially that which contains much decaying 
animal or vegetable matter. Some occur in fresh water, 
many in the sea. A few live in moist earth and more are 
parasitic in other and higher animals, where they may 
be productive of disease. 

As they are the simplest of animals, so they are regarded 
by naturalists as the oldest, it being believed that at one 
time that they, together with the simplest plants, were 
the only forms of life upon the earth. 

The Protozoa are divided into three classes : Rhizopoda, 
Infusoria, and Sporozoa. 

Class I. — Rhizopoda. 

These are the least specialized of the Protozoa and in 
them cell organs are few. There is no denser external layer 
to the body and hence they are able to thrust out lobes 
or pseudopodia from any part of the surface and to retract 
them at will. By means of these pseudopodia the animals 



148 



SYSTEMATIC ZOOLOGY. 



move about and obtain their food. The subdivisions of the 
class are based primarily upon the character of the pseudo- 
podia. 

Order I. Lobosa. With broad pseudopodia few in 
number. Best known is the genus Amoeba of fresh water. 
Other genera have shells (fig. 3). 




; v££ 



Fig. 3. — Difflugia. A lobose 
Rhizopod with a shell of 
grains of sand. Common 
in fresh water. 



Fig. 4. — Foraminifera. 
extended pseudopodia 



chambered shell of Globigerina. 



A, Biloculina with 
(after Schultze); B, 



Order II. Foraminifera. Numerous slender pseudopo- 
dia which branch and unite to form networks. Nearly 
all are marine. Most species form calcareous shells which 
in many species increase with growth by adding addi- 
tional chambers to the original one. There is a terminal 
aperture for the extension of the pseudopodia and in many 
minute pores through the sides of the shell. These forms 
occur in large numbers in certain seas and the dead shells 
are forming thick layers at the bottom of the ocean. They 
have done the same in ages past and in various parts of 
the earth are thick beds of limestone largely built up from 
their dead shells. Indeed they are the largest contributors 
to the formation of rock of all animals. 



PROTOZOA. 



149 



Order III. Radiolaria. Numerous simple thread-like 
pseudopodia which do not interlace. The structure of the 
central mass of protoplasm is complicated. Most of the 
species form silicious skeletons of beautiful forms (fig. 5), 




Fig. 5. — A Radiolarian, Haliomma erinaceus (from Hertwig). a, external 
latticed spherical skeleton; ck, central capsule; i, internal skeleton; n, 
nucleus ; wk, extra capsular protoplasm. 

the rods of which run to the centre of the cell. Like the 
Foraminifera these live at the surface of the ocean and 
contribute to the ooze at the bottom of the sea. 



Class II. — Infusoria. 

These animals, which receive their name from their 
abundance in infusions of vegetable matter, have the 
body covered with a denser portion or cuticle, so that 
pseudopodia cannot be protruded. Instead they have 
delicate permanent processes, which when few in number 
and long and whip-lash-like are called flagella, when 
short and numerous are called cilia. Both are capable 



150 



SYSTEMATIC ZOOLOGY. 



of motion and by their aid the animal swims through 
the water, or, if fixed, creates currents which bring food 
to it. Like other Protozoa these forms multiply by 
dividing into two or more individuals, this process in 
some being preceded by conjugation, which from its im- 
portance from a theoretical standpoint needs a few words. 
Conjugation is the union of two individuals. In many 





Fig. 6. — A flagellate Infusorian, 
Chilimonas paramoecium (after 
Biitschli). n, nucleus; oe, 
oesophagus; v, contractile vac- 
uole. 



Fig. 7. — A ciliated Infusorian, Stylo- 
nichia mytilus, in process of division 
(after Stein), a, anus; cv, contractile 
vacuole; m, mouth; ma, macronucleus ; 
mi, micronucleus ; nm, new mouth. 



cases the conjugating individuals are equal in size and 
the union is temporary, the essential feature being an 
exchange of nuclear material. Here we have the lowest 
expression of sexuality, but without differentiation of 
sex. With others the conjugating individuals are un- 
equal in size and the fusion is permanent, the resulting 



PROTOZOA. 151 

compound later dividing into two equivalent individuals. 
Here we have true sexuality. 

The classification of the Infusoria is based upon the 
character of the appendages developed from the body. 
Only the two most prominent groups are mentioned. 

Order I. Flagellata. With one or more flagella (fig. 6). 
Some of these forms are clearly animal, while allied species 
are claimed by the botanist. Some are naked, some have 
collars around the flagellum, and others have cases in which 
the animal is placed. Some swim freely and some are at- 
tached; among these latter colonies consisting of several 
or many individuals are common, these arising by incom- 
plete division. Some live in fresh water, others are marine. 

Order II. Ciliata. Numerous cilia either over the whole 
body or restricted to certain areas. The ciliates occur 
in both salt and fresh water and include some of the largest 
Protozoa. Some swim freely, some creep about on large 
modified cilia (fig. 7), and some are attached. Most 
familiar are the genera Paramceciwn, Vorticella, and Stent or. 

Class III. — Sporozoa. 

These degenerate forms were long neglected, but within 
recent years they have attained great prominence because 
of the relations to certain diseases. All are parasitic 
inside other animals. They lack all external cell-organs, 
and most of them, except at the time of reproduction, 
are without powers of motion. The name Sporozoa refers 
to the fact that in reproduction these Protozoa break up 
into a number of small bodies called spores. Most 
important of the Sporozoa is Plasmodium laverani (fig. 8), 
which is introduced into the human blood by mosquito 
bites and there lives parasitic in the blood-corpuscles, 



152 SYSTEMATIC ZOOLOGY. 

causing malaria. Mosquitoes in biting a malarial patient 
take the parasite with the blood and can then infect 




Fig. 8. — Four stages in the history of the Sporozoan which causes malaria. 
In A a spore has just entered a blood-corpuscle; in B it has increased in 
size ; in C it is beginning to break up into spores ; in D the spores are fully 
formed. The blood-corpuscle now breaks up and the spores are set free to 
enter other corpuscles. 

another person. More recently discovered is the Sporozoan 
which lives in the tissue-cells and is the cause of the 
disease smallpox. 

Summary of Important Facts. 

1. The Protozoa are microscopic animals, each con- 
sisting of a single cell. 

2. They may possess cell-organs as pseudopodia, cilia, 
nagella, cell-mouth, contracting vacuole. 

3. Each cell performs all of the functions of life; there 
is no differentiation between the cells. 

4. The Protozoa reproduced by division. Incomplete 
division may result in the formation of colonies. 

5. The Protozoa are divided into Rhizopoda, Infusoria, 
and Sporozoa. 

6. The Rhizopoda have no external cuticle, and con- 
sequently may take food at any point of the surface. 
They possess pseudopodia. Many form skeletons of lime 
or silica. 

7. The Infusoria have a cuticle; in most there is a 
cell-mouth for taking food. They have cilia, flagella, or 
tentacles. 



PROTOZOA. 153 

8. The Sporozoa are parasites in other animals, in 
which they often cause disease. They lack all external 
cell-organs and are capable of motion only in the imma- 
ture condition. 

9. A sporozoan, Plasmodium laverani, causes malaria; 
it is introduced into man by mosquitoes. 



METAZOA. 



All remaining divisions or groups of animals are united 
under the name Metazoa for the following reasons: A 
careful consideration of their structure leads to the con- 
clusion that in all the body is of appreciable size, and 
that in each and every one certain portions or organs are 
specialized for the performance of certain functions neces- 
sary in the economy of the individual. Thus we find in all 
reproductive organs which have solely to do with the 
perpetuation of the species ; in all (except a few degener- 
ate parasites) there is an opening 
(mouth) for taking in of food and an 
alimentary tract for its digestion; in 
all there is a more or less distinct ner- 
vous system; and in all parts of the 
body are more or less specialized for 
respiration. 

A little deeper insight leads to 
another conclusion which further justi- 
fies the group of Metazoa. The body 
is composed of layers, at least two in 
number, one on the outside forming the 
skin, and a second on the inside forming 
the lining of the digestive tract. To 
these two layers are 'riven names, ectoderm and entoderm 
(fig. 9), meaning respectively outer and inner skin. 

154 




Fig. 9. — Diagram of a 
two-layered animal, 
based upon a hy- 
droid. ec, ectoderm ; 
en, entoderm. 



METAZOA. 155 

In the Coelenterata all of the functions of the animal are 
performed by either one or the other of these two layers. 
In all the other divisions a third layer occurs between 
ectoderm and entoderm — the mesoderm (middle skin) — 
and this mesoderm takes some of the functions which are 
divided between the ectoderm and entoderm of the Coelen- 
terata. The study of the development of these three- 
layered animals shows a very interesting fact. At first 
there are but two layers in the body, and later the meso- 
derm develops between these two. In other words, all of 
the higher Metazoa pass through a stage in which they 
exhibit a ccelenterate condition. 

These three layers reach their highest condition in the 
Vertebrates, and it may be interesting to see how the 
various structures which are found in a shark, a bird, and 
a rat are related to these layers. 

To the ectoderm belong the outer layer of the skin, 
the outer layer of scales, the hair, feathers, sweat-glands, 
the enamel of the teeth, the nervous system, the sensory 
portions of sensory organs, and the lens of the eye. 

The entoderm furnishes the lining of the alimentary 
canal, the notochord, gills, tracheal lining, lungs, liver, 
pancreas, urinary bladder. 

The contributions of the mesoderm to the body are 
more extensive. They include the deeper layers of the 
skin, fat, muscles, connective tissue, cartilage, bones, liga- 
ments, blood-vessels, blood, the lining (pleural, pericardial, 
and peritoneal membranes) of the body-cavity, the deeper 
layer of the scales, the dentine of the teeth, the outer 
layers of the alimentary canal, and the reproductive and 
excretory organs and their ducts. 

If we study any part of any one of the Metazoa under 
the higher powers of the microscope — having first treated 



156 SYSTEMATIC ZOOLOGY. 

it so as to bring out details — we will discover another 
fact of great importance. Every one of these animals 
will be found to be made up of small parts or cells, essen- 
tially like each other, just as the wall of a building is built 
up of separate bricks. Each of these cells is micro- 
scopic in size, with an average diameter of about -g-^Vo" °f 
an inch; and each consists of a semi-fluid protoplasm, in 
the centre of which is a nucleus. Now, since each and 
every metazoan is built up of cells, we may speak of the 
Metazoa as many-celled animals. 

These cells vary greatly in shape, but no matter how 
different they may appear at first sight, they all agree 
with the description given in the last paragraph. Some 
may be spherical, others cubical or flattened, and still 
others branched, yet in all there is the same nucleus. 
Cells of the same general shape are united together to 
form tissues, so that we have bone-tissue made up of what 
may be called bone-cells, muscular tissue of muscle-cells, 
and nervous tissue of nerve-cells, etc. 

In the Metazoa the tissues are built up into organs for 
the performance of certain purposes; and usually a single 
organ is composed of several kinds of tissues, while the 
same kind of tissue may reappear in different organs. 
Thus the hand of man is an organ of grasping; in it we 
find muscular, bony, connective, and nervous tissues; 
while in the heart of the shark muscular, connective, and 
nervous tissues appear. 

The Metazoa are subdivided into groups, or phyla, which 
may be arranged in order of their complexity in the 
following manner : 

Phylum I. — Spongida. 
Phylum II. — Ccelenterata. 
Phylum III. — Vermes. 



METAZOA. 157 

Phylum IV. — Mollusca. 
• Phylum V. — Arthropoda. 
Phylum VI. — Echinoderma. 
Phylum VII. — Chord ata. 

Summary of Important Facts. 

1. The Metazoa are many-celled animals. The cells 
are differentiated and arranged in layers, no one cell or 
layer performing all the vital functions. 

2. An outer layer (ectoderm) and an inner layer (en- 
toderm) are always present; a middle layer (mesoderm) 
between the other two occurs in most Metazoa. 

3. The ectoderm is protective, nervous, and sensory; 
the entoderm is concerned in digestion; the mesoderm 
usually gives rise to muscular, skeletal, circulatory, and 
excretory organs; respiration may be effected by either 
ectoderm or entoderm. 

4. The layers are usually distributed in tissues, each 
tissue being composed of essentially similar cells. 

5. Organs may consist of a single tissue or of a com- 
plex of tissues. An organ is a structure for the perform- 
ance of a definite function. 



Phylum I.— SPONGIDA (Porifera). 



Sponges differ from other animals in so many respects 

that for a long time naturalists were uncertain as to whether 

they were animals or plants, but this matter has long been 

settled beyond dispute. There is, however, more ques- 

tion as to the position of these forms 

in the Animal Kingdom. They have 

been regarded as colonial Protozoa, as 

members of the Ccelenterata, and as a 

distinct group, or phylum, the position 

given them here. 

The structure of a sponge can be 
best understood by starting with the 
simplest forms (fig. 10). One of these 
is a vase-like structure with a central 
or gastral cavity communicating with 
the exterior by a terminal opening, the 
osculum. Through the sides of the vase 
are numerous small openings or pores 
(whence the name Porifera) , and through 
these water, carrying with it oxygen 
and small food particles, is drawn, the 
waste-water passing from the gastral 
cavity by means of the osculum. Such 
a sponge is the so-called Ascon type. 
If now the gastral cavity develop pouch-like folds in 

158 




Fig. 10. — A simple 
(Olynthus) sponge 
(after Haeckel). One 
side has been broken 
away to show the 
interior, e, spicules; 
i, eggs ; o, osculum ; 
p, pores; u, gastral 
cavity. 



SPONGES. 159 

its walls the result will be the formation of numbers of 
chambers or ampullce around a central cavity. With this 
modification the ampullae become the seat of digestion, 
while the central cavity has no longer that function but 
becomes a cloaca, a part of the passage leading the waste- 
water to the exterior. This is the Sycon type. Further 
complications are introduced by the formation of branch- 
ing incurrent canals leading from the pores to the ampulla? 
and similar excurrent canals connecting the ampullae with 
the cloaca. 

There are considerable difficulties in homologizing the 
layers of the sponges with those of other Metazoa. The 
digestive cavities (gastral cavity, ampulla?) are lined with 
an entoderm of collared flagellate cells, while the rest of the 
body is made up of connective tissue covered by an epi- 
thelium of flattened cells. In this connective tissue the 
eggs and sperm are formed (fig. 10), and usually the em- 
bryos remain here until well advanced in development. 

A few sponges have no skeleton, but most species have a 
firm support for the soft parts, arising in the connective 
tissue. This skeleton may consist of small particles 
(spicules) of carbonate of lime or of silica, often much like 
crystals in form; or of fibres of a horny substance; or 
again, both spicules and fibres may occur together. In 
the sponges of the stores we have nothing but the horny 
fibres, all of the flesh having been washed away; but in 
this skeleton we can trace roughly the systems of canals, 
the cloaca, and the osculum. 

Sponges reproduce by budding and by eggs. In budding 
small outgrowths occur, and these gradually become 
larger, and finally an osculum is formed. From the eggs 
are formed little free-swimming embryos, which later 
settle down and grow into the adult. 



160 SYSTEMATIC ZOOLOGY. 

Sponges are largely marine, only a few forms, and 
these of no economic importance, occurring in fresh water. 
The sponges of commerce come from the Mediterranean, 
the Red Sea, and Florida and the West Indies. They are 
brought up by divers or by hooks which are dragged over 
the bottom. The fleshy portions are allowed to decay, 
then the skeleton is washed, and the sponges are packed 




Fig. 11. — Sponge (Dactyocalyx). From Liitken. 

in bundles for the market. There are different grades of 
elasticity and fineness of fibre and consequently different 
values. The finest sponges come from the eastern part 
of the Mediterranean. Sponges occur as fossils, espe- 
cially in the Cretaceous rocks. 

There are two great groups of sponges. In the first, 
called Calcarea, the skeleton is composed of carbonate of 
lime ; in the second, Silicea, there is sometimes a skeleton 
consisting of silica (quartz), sometimes of horny fibres 
(here belong the sponges of commerce), sometimes of 
both horny fibres and siliceous spicules; and again, there 
are a few forms which have no skeleton. 



SPONGES. 161 

Summary of Important Facts. 

1. Sponges have one or more digestive cavities (ampullse) 
connected with the external world by numerous incurrent 
pores and one or more ex current oscula. 

2. Water flows through these pores and the connecting 
canals, bringing nourishment to the animal; waste is car- 
ried away by the osculum. 

3. Sponges reproduce by eggs and by budding. There 
is no alternation of generations. 

4. A skeleton is usually present; according to its nature 
sponges are divided into Calcarea and Silicea. 



Phylum II.— (XELENTERATA. 

The Coelenterata and the Echinoderma were formerly 
united into a group Radiata, the basis of association being 
the radiate type of structure so noticeable in a starfish or a 
coral. Later studies showed that these two divisions had 
very few points in common, and that the differences be- 
tween them were very great. 

In the Coelenterates there is but a single opening into 
the digestive tract, which thus serves at once for mouth 
and vent. Through it all food enters, and all indigestible 
portions are cast out. The mouth connects with the 
digestive tract, which extends to all parts of the body, so 
that the food is brought close to every portion, there 
being no circulatory apparatus. There is no body-cavity 
distinct from the digestive tract. The wall of the body is 
but two layers of cells in thickness, with between them 
a third layer, sometimes thin and without cells, some- 
times thick and gelatinous, with scattered cells in the 
jelly. This third layer is called the supporting layer, or 
mesogloea. Around the body, frequently close to the 
mouth, is a circle of tentacles, and on these abound some 
structures which need a slight description — the nettle- 
cells. 

These nettle-cells, fig. 12, are small bodies which occur 

all over the body, but are especially numerous upon 

the tentacles. Each is in reality a sac, one end of 

162 




CCELENTERATA. 163 

which is drawn out into a long and slender tube coiled 
up inside of the rest. These nettle-cells can be ' dis- 
charged' by the animal, the discharge consisting in a 
forcing out of the tube in the same way in which one 
may blow out the inturned finger of a 
glove. These cells contain a strongly 
irritant poison, and at the discharge 
this poison escapes. These nettle- 
cells furnish a means of defense, and 
they are also used in obtaining food, 
the poison being strong enough to 
paralyze small animals instantly. In 
some forms it is strong enough to 
affect man. For instance, the tenta- FlG i 2 .—T discharged 
cles of the Portuguese man-of-war will ^faroi^d th^ST* 
quickly raise a bright-red ridge on 
the hand or arm of man and produce an almost intolerable 
burning sensation in the parts thus touched. 

In many Ccelenterates there is no specialized nervous 
system, the general surface of the body having sensory 
and nervous powers. In others there is a central nervous 
system arranged in a ring around the body; and some 
of the jelly fishes have organs the structure of which 
leads to their being regarded as simple types of eyes and 
ears. 

Some move about freely, some are as firmly fixed as is 
any plant; but both fixed and free conditions may occur 
in the life-history of a single species. Some of the fixed 
forms may be single, but others will form buds upon 
the sides or from the point of attachment; and then 
these buds will grow tentacles, while a mouth will open 
at the tip of each, so that there results a compound animal 
with many parts which are more or less complete repeti- 



164 SYSTEMATIC ZOOLOGY. 

tions of each other. Such a compound condition is 
known as a colony, and the separate members of the 
colony as hydranths or zooids. Most of the free forms 
are known as jellyfish or medusas. As a rule a medusa 
consists of a bell- or umbrella-shaped disc ; fig. 13; from 




Fig. 13. — Medusa (Melicertum campanula), enlarged. 

the lower surface (corresponding to the handle of the 
umbrella or the tongue of the bell) projects a proboscis, 
at the tip of which is the mouth. Around the margin 
of the bell are the tentacles, and these, compared to the 
snaky locks of the mythical monster, have given rise 
to the name. The medusae swim through the water by lazy 
motions of the umbrellas, feeding upon whatever may 
come in their way. The medusae are the sexual stage. 
All of the Ccelenterates reproduce by means of eggs, 



CCELENTERA TA. 165 

but, besides, most forms have the power of forming buds 
which grow into new individuals, sometimes like, in 
others greatly different from, the parent; the buds some- 
times remaining attached, as often separating from the 
parent. With very few exceptions the Coelenterates are 
marine. The phylum is divided into three classes: Hy- 
drozoa, Scyphozoa, and Ctenophora. 

Class I. — Hydrozoa. 

The Hydrozoa are mostly small, and among them 
colonial forms predominate. They are distinguished 
from the other classes by the absence of an inturned 
oesophagus and of well-developed radial partitions divid- 
ing the digestive cavity. The tentacles also are solid. 
In their life-history there are frequently some wonderful 
changes, and to describe these we may follow the life- 
cycle of Pennaria, described in the laboratory work. 

From the egg there hatches out a little oval, free-swim- 
ming embryo, which soon attaches itself by one end to 
some submerged rock, while a mouth breaks through at the 
other, and tentacles grow out around the sides of the body. 
When a mouth is formed feeding and growth are possible. 
As the animal grows larger little buds appear on the sides, 
and these, forming mouths and tentacles, grow into hy- 
dranths like the parent. These buds never become free, 
but the whole colony thus formed has a common digestive 
tube by which all are connected. On the outside a tubular 
horny protecting sheath, the perisarc, is developed. After 
a while buds appear on the sides of the hydranths, and 
these have a much different history, for they develop into 
free-swimming jelly fishes. At other times the medusa 
buds may develop from the stalk (fig. 14, mk) or from 
the root-like stolons, which connect the parts of the colony 



166 



SYSTEMATIC ZOOLOGY. 



In these jellyfishes (fig. 14, m) branches of the digestive 
tract run to the margins of the umbrella, where they 
connect with a ring canal which runs around its rim near 




Fig. 14. — A Hydroid (Bougmnvillea). After Allman, from Lang, h, hydranth; 
mk, medusa-buds; m, a free-swimming medusa. At the base are seen the 
root-like stolons connecting the colony together. 

the bases of the tentacles. These hydrozoan medusae can 
be recognized by having the opening of the bell partially 
closed by a thin membrane (velum) shown in the figure. 
These medusae separate from the colony and swim freely 
through the water, and they produce eggs from which 
are developed other colonies. 

Here is a point which needs emphasis. From the egg is 
developed a hydranth which by budding gives rise to 



CCELENTERATA. 167 

numerous other hydranths, and each of these in turn by 
budding may produce several medusae. In other words, 
we have here an animal which reproduces asexuafly. 
These medusae are the sexual forms, and they produce 
eggs which grow not into other jellyfishes but into the 
fixed forms. This phenomenon is known as an alternation 
of generations, the young resembling not the parent, but 
rather the grandparent. 

Order I. — Hydride. 

Here belongs the fresh-water Hydrozoan — Hydra — in 
which there is no medusa stage, the animals producing 
eggs which develop directly into other Hydrae. The 
fresh-water Hydrae, which are green or brown in color, 
and about J inch in length, are common in fresh water, 
attached to plants, stones, etc. 

Order II. — Hydromedus^. 

Pennaria is typical of this group. In most of the species 
there is that alternation of fixed and free-swimming forms 
which has already been described. In the fixed stage the 
colony is usually protected by a perisarc which occasion- 
ally may be developed into cups (thecal) protecting the 
hydranths . On the other hand, some of these Hydromedusae 
exist only as jellyfishes, the eggs which they produce 
developing directly into other jellyfishes, while in others 
the medusae do not separate from the colony, but, remain- 
ing attached, retain more or less clearly the features of 
the jellyfish, and always produce the eggs. The Hydro- 
medusae are abundant in all seas, and are among the most 
beautiful and interesting of all the animals with which 
the naturalist has to deal. Only two or three species 
occur in fresh water. 



168 SYSTEMATIC ZOOLOGY. 

Order III. — Siphonophora. 

These may be defined as colonies of medusae, arising by 
budding. In these colonies the medusae become special- 



^2X28^ 





Fig. 15. — Diagram of a Siphono- 
nhore. c, covering scale; d, 
digestive sac ; /, float ; m, mouth 
of feeding individual; r, repro- 
ductive bell ; s, swimming-bell ; 
t, tentacle. 



Fig. 16. — Portuguese man-of-war 
(Physalia). After mgassiz. 



ized in different directions. This specialization in some 
forms may go so far (figs. 15, 16) that we have the jelly- 



CCELENTERA TA. 169 

fishes modified into (1) a float supporting the colony; 
(2) swimming-bells by means of which it moves; others (3) 
for feeding, still others (4) for digestion, and again others 
(5) for reproduction. In all of these only that part of 
the medusa which is necessary for the function is retained. 
Thus in the figure it will be seen that the swimming- 
bells have no proboscis, the feeding individuals consist 
of proboscis alone, etc. Usually one or more of these 
modified medusae is lacking from the colony. The most 
familiar of the Siphonophora is the ' Portuguese man-of- 
war' (fig. 16), which occasionally drifts on our shores. 
In this beautifully-colored species the float is large and 
the swimming-bells are absent. 

Class II. — Scyphozoa (Sea-anemones, Corals, 
Medusae, etc.). 

While the Hydrozoa may be likened to a double bag, 
the two bags corresponding to the ectoderm and entoderm 
(p. 154), the Scypho'zoa, fig. 17, might be compared to the 
same bags, with the mouth turned inwards, and extend- 
ing as a tube for some distance into the interior. In 
this way there arises a short food-tube or oesophagus lead- 
ing from the mouth to the digestive cavity. The diges- 
tive cavity itself is subdivided by partitions or septa 
radially arranged so that there is a central chamber and 
connected with it chambers between the septa. To these 
characteristic features may be added others. Thus there 
is a circle of (usually hollow) tentacles surrounding the 
mouth, and the edges of the septa bear long thickened 
threads, the mesenterial filaments, which are digestive in 
function. The septa greatly increase the surface of the 
digestive cavity so that the food dissolved by the secre- 



170 



SYSTEMATIC ZOOLOGY. 



tions of the mesenterial filaments can be more readily 
absorbed. Further details of structure are better given 




Fig. 17. — Model of a Scyphozoan, part of the wall cut away to show the internal 
structures. At the top is the oral disc with three tentacles. The oesophagus 
extends, in the centre, into the digestive cavity, the cavity being subdivided 
by radial septa. In the cut edges of the walls and septa the ectoderm is left 
white, the entoderm is divided into blocks. 



in treating of the two subclasses into which the Scyphozoa 
are divided, merely saying here that all are marine. 



CCELENTERATA 



171 



Subclass I. — Actinozoa (Sea-anemones and Corals). 

In these the animal is usually fixed. It never swims 
freely except in the embryonic stages. The body is more 
or less columnar, with a base for attachment and an oral 
disc inside the circle of tentacles, in the centre of which 
is the oval or slit-like mouth. Inside, the septa are well 
developed, and attached to these are, besides the mesen- 
terial filaments, long cords of nettle-cells which can be 
protruded through the mouth or through small openings 





Fig. 18. — Diagram of a bit of coral to show 
the way in which the polyps are con- 
nected. The coral is black, the digestive 
cavity shaded. In nature the digestive 
cavity is divided into small canals con- 
necting the different polyps. 



Fig. 19. — Section of a 
coral cup showing 
the calcareous septa. 
After Pourtales. 



in the walls of the body. In some the individuals 
(polyps) are separate; in others the individuals repro- 
duce by division or by budding, and the new polyps thus 
formed never completely separate from their parents, so 
that large aggregations or colonies result. In these one 
can distinguish the mouths, and usually the tentacles, of 



172 SYSTEMATIC ZOOLOGY. 

the individual polyps, but the division does not affect the 
digestive tract, so all are connected, and the food which is 
taken in at one mouth may serve to nourish any part of 
the whole colony (fig. 18). In some the outer surface 
of the body is naked, but in many of the solitary and in 
most of the colonial forms the base or both base and 
column secrete carbonate of lime, thus forming a solid 
support for the body. This solid support is the well- 
known coral. In most specimens of coral one can readily 
recognize the cups (fig. 19) in which the separate polyps 
were situated; and in these cups, in most cases, are calcare- 
ous partitions much like the septa of the soft parts.* As 
long as the colony remains alive it is constantly budding 
off new polyps, and thus the colony and the coral grow. 
Those species which live in cold water produce but little 
coral, but in tropical waters coral-producing forms abound, 
and by their combined secretions the coral islands are 
made. 

The great majority of the Actinozoa may be subdivided, 
according to the number of septa, into two orders: 

Order I. — Octocoralla. 

In these the separate polyps are small, and each has but 
eight septa and eight tentacles. They produce but little 
coral, but rather those kinds of coral which are known as 
sea-fans and sea-whips. One form is especially notice- 
able, since it produces the precious red coral so often carved 
into beads, etc. 

* These calcareous septa do not coincide with, but alternate in 
position with, the fleshy septa. 



CCELENTERATA. 



173 



Order II. — Hexacoralla. 

As the name indicates, the septa and tentacles here 
occur in multiples of six. Here belong all the sea-anem- 
ones and the true corals, which produce coral-reefs and 




Fig. 20. — Sea-anemone (Metridium). From Emerton. 

islands. The reef -building species are limited in their 
distribution by temperature, for they cannot live where 
the temperature of the water falls below 60° Fahr. (13° C.) . 



Subclass II. — Scyphomedus^ (Jellyfishes). 

At first sight the Scyphomedusse differ greatly from 
the Actinozoa. They are free-swimming forms (medusae) 
in which the body is umbrella-shaped, the mouth is at the 
end of a proboscis, and all is semitransparent, Yet when 



174 SYSTEMATIC ZOOLOGY. 

the details of structure are analyzed there are found the 
same in turned oesophagus, the same septa and filaments, 
and the same tentacles; and hence these forms must be 
somewhat closely associated with the sea-anemones, while 
these same features together with the absence of a velum 



Fig. 21. — Common white Jellyfish (Aurelia). After Agassiz. 

mark them off from the Hydrozoan jellyfishes (p. 166). 
While some are small, others become veritable giants, the 
large blue jellyfish of the New England coast sometimes 
measuring seven feet across, its tentacles streaming be- 
hind for a hundred feet as it swims through the water. 

Subclass III. — Ctenophora. 

These forms, which are also called jellyfishes, differ 
from the other ccelenterates in several respects. The body 
is usually globular, instead of umbrella-shaped, and bears 
on the surface eight rows, like meridians (fig. 22, c) of 
vibratile organs, each row being composed of numerous 
series of cilia, arranged much like the teeth of a comb 



CCELENTERATA. 



175 



(ctenophora = comb-bearers). There is no proboscis, the 
wide mouth, with an ectodermal oesophagus, being at one 
pole of the body and leading to a digestive tract which 




Fig. 22. — Diagram of a Ctenophore. c, rows of combs ; g, branches of digest- 
ive tract; i, "intestine"; m, mouth; o, oesophagus; s, sensory plate ; t, ten- 
tacle ; tc, tentacle sheath ; y, oesophageal vessel. 



branches again and again (g), so that at last a portion 
underlies each row of combs. There are no nettle-cells in 
these forms and there never occurs any alternation of 



176 SYSTEMATIC ZOOLOGY. 

generations. The ctenophores are all marine, are per- 
fectly transparent and so delicate in structure that it is 
almost impossible to preserve them, some being torn by 
strong currents of water. They are among the most 
voracious of animals. As a rule few measure more than 
three or four inches in diameter. 



Summary of Important Facts. 

1. The Ccelenterata and the Echinoderma were for- 
merly united as a group Radiata on account of their 
radiate structure. 

2. The Ccelenterata have but a single opening to the 
digestive tract; there is no body-cavity; the body-wall 
is composed of ectoderm and entoderm with a supporting 
layer between them. 

3. The nettle-cells are especially characteristic. 

4. Reproduction is by eggs and by fission, or budding. 

5. Some buds may become free and form medusae and 
there is frequently an alternation of generations. 

6. The Ccelenterata are divided into Hydrozoa and 
Scyphozoa. 

7. The Hydrozoa lack an inturned oesophagus. They 
have frequently an alternation of fixed or polyp and free 
or medusa generations. 

8. The Hydrozoa are divided into Hydridae, Hydro- 
medusae, and Siphonophora. 

9. The Scyphozoa have an inturned oesophagus; the 
digestive tract is subdivided by radial septa bearing mes- 
enterial filaments. 

10. The Scyphozoa are divided into Actinozoa and 
Scyphomedusse. 



CCELENTERATA. 177 

11. In the Actinozoa there is only the polyp condition 
Most of the species produce coral. 

12. The Scyphomedusce are medusae, the young of which 
are polypoid in character. 

13. The Ctenophora are f ree-swimming ; they lack 
nettle-cells. Most characteristic are the eight meridional 
rows of vibratile combs. 



Phylum III.— VERMES (Worms). 

Under this heading are included a large number of forms 
commonly known as worms, a group incapable of strict 
definition. In general it may be said that they have 
elongate bodies without internal skeleton, without jointed 
appendages, with a marked bilateral symmetry, and dis- 
tinct dorsal and ventral surfaces. Further than this we 
can hardly go in a definition which will at once include all 
worms and at the same time not include other forms. 
Indeed, it is probable that the group is not a natural one 
and that its members should not be associated together. 
Still in an elementary work it is best to follow a con- 
servative course and not confuse the beginning student 
with a number of phyla some of which contain but a few 
inconspicuous forms. Some worms are terrestrial, some 
aquatic, r and some live as parasites on or in other animals. 
Omitting a number of microscopic forms and small groups, 
we may divide the Vermes into four classes: Plathel- 
minthes, or flatworms; Nemathelminthes, or roundworms; 
Annelids, or segmented worms, and Molluscoidea. 

Class I.— PLATHELMINTHES (Flatworms). 

In the flatworms the body is flattened, is without appen- 
dages or skeleton; the mouth when present is on the ven- 
tral surface and no vent occurs. There is no body-cavity 
aside from the digestive tract. Some are leaf -like, others 
are more elongate, and a very few are nearly cylindrical. 
The free-living and some of the parasites have an alimen- 
tary canal, but to this there is only a single opening, the 

178 



WORMS. 



179 



IF 



mouth. Aside from the digestive cavity, the body is solid 
throughout, there being no such body-cavity as occurs 
in the higher worms, the echinoderms and the vertebrates. 
The nervous system consists of a centre, 
or 'brain/ always in the dorsal front por- 
tion of the body, from which nerve-cords 
run to various parts, there being usually 
two long cords which run backwards in 
a nearly parallel direction. Eyes may 
be present on the dorsal surface near 
the brain. 

The capacity of reproduction by di- 
vision is very well developed in many 
species, especially in the non-parasitic 
groups . In these a sec- 
ond mouth will appear at 
about the middle of the 
body, then the body will 
constrict in front of the 
new mouth, and finally 
will divide into two 
worms. Not infrequently 
a new mouth will appear 
in each of the halves be- 
fore the division is com- 
plete, so that 



:I7 




Fig. 23.— Process of di- 
vision in Microstomum. 
After Graff. m, m 2 , 
mouths of successive 
generation; I-V, suc- 
cessive planes of divi- 
sion. 



we can 



Fig. 24.— A Tur- 

^rS a eniargid? have a chain of four or 
even eight animals con- 



nected together, and all 
the result of division of 
a single parent (fig. 23). Besides this reproduction by 
division, reproduction by means of eggs occurs. The Pla- 
thelminthes are divided into three orders — Turbellaria, 
Trematoda, and Cestoda. 



180 



SYSTEMATIC ZOOLOGY. 



Order I. — Turbellaria. 
These are small free-living forms which occur in fresh 
(fig. 24) or salt water, and occasionally in moist earth. 
They are common in our ponds and streams, crawling 
slowly over the bottoms or upon submerged sticks and 
stones. They have a mouth and digestive tract, the 
latter rod-like, three or many branched. 

Order II. — Trematoda. 

. Like the last, these have mouth and digestive tract, but 
they differ in being parasitic on or in other animals, and in 
having sucking-discs (from one to many) developed upon 
the body. Some of them become serious pests. One 
form, the liver-fluke, produces the disease known as 
' liver-rot' in sheep. Other forms occur in man, espe- 
cially in the tropics, being introduced in drinking-water. 
They cause serious sickness. In the case 
of many trematodes the parasite must pass 
into two animals in order to complete its 
life-history, the process being frequently 
complicated by an alternation of genera- 
tions. Thus in the case of the liver- 
fluke, just mentioned, the eggs are laid 
by the fluke while still in the liver; 
they pass out through the bile-duct and 
intestine to the exterior, where they 
hatch a peculiar embryo on the grass. 
This bores into a snail, and by budding 
gives rise to other kinds of parasites, so 
that from a single egg a large number 
Fl stage 5 ofTiveT-flukt of individuals may be produced. The 
Thoma?) P (after nna * sta £ e m the snail is a tailed form, 
the cercaria, fig. 25, which escapes and 
getting on the grass is eaten by sheep, when it drops its 




WORMS. 



181 



tail and changes into the adult fluke, which makes its 
way into the liver. In other cases the change is from snail 
to birds or to frogs ; the host of the immature forms being 
usually a mollusc, that of the adult a vertebrate. 

Order III. — Cestoda (Tapeworms). 

The Cestodes are all parasitic in other animals. They 
differ from the Trematodes in the complete absence of 
mouth and digestive tract, since they absorb their nourish- 
ment through the skin. Usually they have ribbon-like 
bodies, and hence are commonly known as tapeworms 
(fig. 26). At the anterior end are 
the means of attachment (hooks or 
suckers) by which the animal at- 
taches itself to the lining of the intes- 
tine of its host, while usually the 
body becomes broken up into a series 
of joints or proglottids. There is con- 
tinually a formation of new proglot- 
tids near the 'head/ or scolex, while 
the older proglottids, loaded with 
eggs, drop off and are carried out 
with the waste of the digestive 
tract. These tapeworms obtain en- 
trance into the body in the food, 
man usually receiving his from raw or 
partially cooked beef or pork, and 
more rarely from fish. The proglot- 
tids and eggs, passing from the body, 
may fall where they may be eaten by cattle or swine. 
Inside their bodies they undergo partial development in 
the muscles, and then when taken into the human body 
they complete their development. Other vertebrates than 
man possess tapeworms. The cat gets hers from the mouse, 




Fig 



26. — Tapeworm 
( 7V ma ) with proglottids 
from different regions of 
the body, h, head en- 
larged. 



182 



SYSTEMATIC ZOOLOGY. 



the dog his from cattle and rabbits, the sharks from other 
fish, etc. 



Class II— NEMATHELMINTHES. 

In these roundworms the body is long and cylindrical, 
and is covered with a firm, tough cuticle. Usually both 
mouth and vent are present, and the alimentary canal 
runs through a large body-cavity (coelom), being con- 
nected with the body- walls only at the two ends. There 
is never any division of the body into segments. Some 
roundworms live freely in the water, some are parasitic 
in plants, and some infest animals. Among them are to 
be mentioned the vinegar and paste 'eels,' which are 
occasionally found in these substances. Here, too, 
belong the 'horsehair- worms,' which are 
frequently believed to be horsehairs con- 
verted into worms by soaking in water. 
These hairworms are at one period of their 
lives parasitic in insects, especially in 
grasshoppers. Some of the roundworms 
occur as parasites in man. The stomach- 
worms and pinworms of children belong 
to the roundworms, and these obtain 
entrance to the human system only as 
the exceedingly minute eggs are taken 
into the stomach by way of the mouth. 

Worst of all the parasitic Nemathel- 

minthes is the Trichina (fig. 27), which 

, when adult is scarcely an eighth of an 

encysted in human ^^ [ n length, and yet which not inf re- 
muscle. After <=> r J 

Leuckart. quently causes death. Man is usually in- 

fected with them by eating raw or partially cooked pork. 
In the pig they first appear in the alimentary canal, where 




WORMS. 183 

tne mothers bring forth myriads of living young. These 
young burrow outwards into the muscles and there enclose 
themselves in a capsule, where they remain indefinitely. If 
this infested flesh be eaten raw, the capsule is dissolved 
by the stomach, the young are soon born, and they in 
turn wander through the muscles, and, when numerous, 
this boring into the flesh causes severe sickness, and even 
death. The worst epidemic of this disease, known as 
trichinosis, on record occurred near Emmersleben, Saxony, 
in 1884. From one pig three hundred and sixty-four 
persons were infected, and of these fifty-seven died within 
a month. The moral which we have to learn from tape- 
worms and trichina is that our beef and pork should 
never be eaten raw, but should be cooked through. 

Class III. — ANNELIDA (Segmented Worms). 

The earthworm may be taken as a representative of 
this group, all the members of which have a marked 
external ringing or segmentation of the body. This seg- 
mentation also extends to the internal organs, so that the 
whole animal may be regarded as a complex of a number of 
essentially similar segments (also called somites or meta- 
meres). A little more detailed account of the structure 
may be given. The alimentary canal (fig. 28, i) runs 
through the body like an axis, and is suspended by a 
longitudinal membrane, the mesentery (m) above and 
below, while at each constriction of the body a similar 
membrane, or septum (s) binds the canal to the body- 
wall. The result of this arrangement of septa and mesen- 
teries is to divide the body-cavity which surrounds the 
alimentary tract into a series of paired cavities, the 
codomic pouches (c), each pair corresponding to an exter- 
nal somite. The circulatory system consists chiefly of a 



184 



SYSTEMATIC ZOOLOGY. 



dorsal blood-vessel (d) in which the blood flows forward, 
and a ventral vessel (v) in which it flows in the opposite 
direction with pairs of vessels (cv), segmen tally arranged, 
connecting the two. The nervous system is composed 




Fig. 28. — Diagram of trunk somites of an Annelid, am, muscles of aciculi; c, 
ccelom ; cm, circular body muscles ; cv, circular blood-vessels ; d, dorsal blood- 
vessel; i, intestine; Im, longitudinal body muscles; m, mesentery; n, ventral 
nerve cord; na, nephridium; ne, no, parts of parapodium; s, septum; sp, 
splanchnopleure ; t, typhlosole. 

of a centre, or brain, above and in front of the mouth, 
from which a pair of nerve cords (oesophageal commissures) 
pass on either side of the oesophagus to connect with a 
ventral nerve cord (n) which extends the length of the 
body beneath the alimentary canal, and which bears 
nervous enlargements, or ganglia, one pair in each somite. 
Thus it will be seen that the brain is dorsal, the rest 
of the nervous system ventral, to the alimentary canal; 
in other words, the digestive tract passes through the 
nervous system. The excretory system consists of a 
system of organs called, nephridia (na). Typically there 
is a pair of these to each segment. Each consists of a 
tube opening at one end by a funnel-shaped expansion, 



WORMS. 185 

or nephrostome, into the coelom, while at the other end 
it empties to the exterior. Usually the tube is much 
coiled and is enveloped in a network of small blood- 
vessels. The annelids are divisible into several groups 
or subclasses, only two of which need mention here. 

Subclass I. — Cmjtopoda. 

In these the body -cavities (coelomic pouches) are well 
marked, as in the earthworm, and each segment of the 
body bears small bristles (chcetce or setce) which serve as 
locomotor organs. Usually the rings visible upon the 
external surface correspond to the somites. 

Order I. — Polych^hle. 

In these the chaBtse are numerous in each segment and 
are usually borne on fleshy outgrowths (parapodia) from 
the sides of the body, which in 
many forms efficient swimming 
organs. The head (fig. 29) bears 
fleshy feelers, or tentacles, and 
eyes are commonly present. The 
Polychsetes, of which there are 
numerous species, are almost 
entirely marine. For conven- 
ience they may be divided into 

two groups. In the ERRANTIA Fig. 29.-^HeId~aId anterior 

the animal is fitted for a free Ky£ .SJSSSJI* 
life and frequently the mouth PoIychsete - 
is provided with strong jaws, making them to the associated 
life terrible animals of prey. The other group, the Tubi- 
cola or Sedentaria, live permanently in burrows from 
which the head, often furnished with numerous tentacles 
and gills, can be protruded. In life the tentacles are in 




186 SYSTEMATIC ZOOLOGY. 

constant motion drawing small food particles to the 
mouth. As a result of this sedentary life the parapodia 
are often greatly reduced (fig. 39). Many of the Polychsetse 
are brightly colored and some are among the most beauti- 
ful objects in nature. 

In the development of many Polychsetes there occurs 
a larval form known as the trochophore, which bears no 




Fig. 30. — A Tubicolous Polychsete (Amphitrite). At the upper end are the 
tentacles, and just below to the left the gills. 

resemblance to the adult. The body is oval or nearly 
spherical and bears one or more circles of cilia. The 
mouth is at one side, the vent terminal. This becomes 
transformed into the worm by elongation and segmentation 
at the hinder end. The great interest connected with the 
trochophore is that similar larvas occur in other groups ; 



WORMS. 187 

notably in the molluscs, thus showing a remote relation- 
ship between them. 

Order II. — Oligoch^t^. 

In the Oligochsetes the parapodia are lacking, and the 
chsetse, which, as the name indicates, are few in number, 
project directly from the body-wall. Appendages of all 
kinds are usually entirely absent. A few of the group are 
marine, more occur in fresh water, but the great majority 
are terrestrial, and are familiarly known as ' earthworms ' 
or ' angleworms/ the latter name being given from their 
use in baiting fish-hooks. The earthworms burrow in 
the soil, feeding upon decaying vegetable matter in the 
earth. They swallow earth and all, and come to the 
surface to deposit their well-known castings. In this way 
they work over the soil, and are of immense value to 
agriculture, as Darwin has shown in a most interesting 
volume on these lowly forms. Our earthworms are mod- 
erate in size, but in Africa, South America, and Australia 
giant earthworms, four to six feet in length and an inch 
in diameter, occur. 

Subclass II. — Hirudinei (Leeches). 

The leeches have the body-segments ringed, so that one 
examining the outside would conclude that there were 
more segments than are really present. There are no bris- 
tles on the segments, but the hinder end always bears a 
sucking disc, while usually there is a second sucker around 
the mouth. The body-cavity is not distinct, for by the 
great development of the tissues it has been almost en- 
tirely obliterated. There are two great groups of leeches — ■ 
those with jaws around the mouth, and those which lack 
jaws. 



188 



SYSTEMATIC ZOOLOGY. 



The jawless leeches are aquatic, and occur in fresh water; 
more rarely in the sea. They live largely upon fishes, 
feeding upon the mucus covering the body. The jawed 
leeches have three jaws radiating from the mouth, and each 
jaw has its edge finely toothed. With these jaws they are 




Fig. 31. — Diagram of two Polyzoan individuals, one expanded, the other re- 
tracted into its cell (after Delage et Herouard). a, anus; m, mouth sur- 
rounded by the tentacles; o, operculum which closes the cell; r, retractor 
muscle. 

able to cut the skin of vertebrates, upon the blood of which 
they feed. This blood-sucking habit led to the use of 
leeches in medicine in those days when it was believed that 
if a man were sick his cure could be effected by still fur- 
ther weakening him. Most of the jawed leeches live in 



WORMS. 189 

fresh water, but in the warmer parts of the Old World land 
leeches occur in the moist forests, and these form almost 
intolerable pests. 

Class IV.— MOLLUSCOIDEA. 

Under this heading are grouped a few forms, which in 
time past were considered as Molluscs (see p. 193), but 
which are now known to have only superficial resem- 
blances to the clams, etc. There are two orders of these 
Molluscoids. 

Order I. — Polyzoa (Moss Animals). 

The Polyzoa are individually small, but by budding 
they form colonies of considerable size, the tentacles of 
the individuals giving the colony a mossy appearance, 
whence the name Bryozoa (moss animals) often given them. 




Fig. 32. — Diagram of a Brachiopod. b, tentacles around mouth, m* i, intes- 
tine; the shell black, the stalk to the right. 

These tentacles surround the mouth in a more or less modi- 
fied circle, and by them the animals obtain their food. 
The body is sac-like, and the alimentary canal is bent upon 
itself so that the vent is near the mouth. Many of the 
colonies secrete an external skeleton, which may be horny 
or calcareous. Most of the Polyzoa are marine, but a 
few occur in fresh water. 



190 



SYSTEMATIC ZOOLOGY. 



Order II. — Brachiopoda (Lamp-shells). 

From the fact that the Brachiopoda possess a bivalve 
shell, these forms were formerly included among the 
molluscs near the clams. A little examination, however, 
shows that the resemblance between them is but slight. 
The two valves of the Brachiopod are unequal in size, and 
are dorsal and ventral, rather than right and left, as in the 
clams. Near the point where the two parts (valves) are 
hinged together there is usually an opening * in the larger 
valve through which a fleshy peduncle or stalk projects, 
by means of which the animal is 
fastened to some support. In- 
side the valves, which can be 
closed by muscles, are the prin- 
cipal organs. Near the mouth 
are found a number of delicate 
tentacles (much like those of the 
Polyzoa), the disc which bears 
them being frequently rolled into 
a spiral. The alimentary canal is bent, but a vent is 
occasionally lacking. 

The Brachiopods are all marine. There are few in 
existing seas; but they are among the oldest inhabitants 
of the earth, for the shells are found fossil in great num- 
bers in all rocks from the earliest down to the present 
time. 

Summary of Important Facts. 

1. The group of VERMES is not a natural one, but an 
association for convenience. Its members are bilaterally 
symmetrical and have distinct dorsal and ventral sur- 

* In some the peduncle extends from between the valves instead 
of having a special opening. 




Fig. 33. — A New England 
Brachiopod ( Terebratulina 
septentrionalis ) . 



WORMS. 191 

faces, but no general definition can be formulated for 
them. 

2. The chief groups of Vermes are Plathelminthes, Ne- 
mathelminthes, Annelida, and Molluscoida. 

3. The Plathelminthes have no body-cavity and only 
one opening (mouth) to the digestive tract, when this is 
present. 

4. The Plathelminthes are divided into Turbellaria, 
Trematoda, and Cestoda. 

5. The Trematoda are parasitic on or in other ani- 
mals, often causing serious disease. They have a three- 
branched alimentary canal, and adhere to the host by 
suckers or hooks. 

6. Many trematodes pass through two hosts and present 
also an alternation of generations in their life-history. 

7. The Cestoda are all internal parasites and have lost 
the digestive system. 

8. Many become broken up into proglottids, new pro- 
glottids forming in front while the older ones at the 
hinder end drop off when mature. 

9. They frequently have an alternation of hosts. Man 
gets his cestode parasites (tapeworms) from the cow and 

Pig. 

10. The Nemathelminthes have cylindrical bodies, and 
a complete alimentary canal (with mouth and anus) which 
runs through a large undivided body-cavity. 

11. They show no segmentation of the body and repro- 
duce solely by eggs. 

12. They are largely parasites. The Trichina is one of 
the worst of human parasites, frequently causing death. 

13. The Annelida have segmented bodies with external 
ringing of the body and a division of the body-cavity into 
paired pouches. 



192 SYSTEMATIC ZOOLOGY. 

14. The nervous system consists of a brain and a pair 
of ganglia in each somite. The oesophagus passes through 
the nervous system between brain and ventral cord. 

15. The Annelida embrace the Chsetopoda and the 
Hirudinei. 

16. The Chcetopoda have well-developed body-cavity, 
and bristles on each segment, the bristles being frequently 
supported by fleshy parapodia. 

17. The Hirudinei have reduced body-cavity and lack 
setae and parapodia. 

18. The Molluscoidea were formerly regarded as mol- 
luscs. They have a complete alimentary canal and a 
circle of tentacles surrounding the mouth. 

19. The Molluscoidea are divided into Polyzoa and 
Brachiopoda. 

20. The Polyzoa reproduce by eggs and by budding, 
the result of the latter being to produce large colonies. 

21. The Brachiopoda have a bivalve shell, the two valves 
being dorsal and ventral. They are attached by a ped- 
uncle and reproduce solely by eggs. 

22. The few existing Brachiopoda are marine. In past 
time they were far more numerous, and fossil brachio- 
pods are abundant in the older rocks. 



Phylum IV.— MOLLUSCA. 



Oysters, clams, snails, and cuttlefish may be taken as 
examples of the ten thousand different species which are 
known as molluscs. The name comes from the Latin 
mollis, soft, and alludes to the fact that, aside from the 
shell, the body has no conspicuous hard parts. This, how- 
ever, is a point of no real importance in classifying animals. 

Molluscs vary greatly in appearance ; but if we carefully 
compare the points which all possess in common, we can 
construct an ideal mollusc, from which any form may be 
derived by additions here and modifications there. Such 
a typical mollusc is described below (fig. 34). 




Fig. 34. — Transverse and longitudinal sections of a schematic Mollusc, a, auri- 
cle; c, cerebral ganglia; d, digestive tract; /.foot; g, gill; h, heart; i, intes- 
tine; I, liver m, mouth; n, nervous system; p, pedal ganglia; pc, pericar- 
dium; s, stomach; v, vent (in left figure, ventricle). 

The body is saccular, and bilaterally symmetrical. 
There is, above, a conical visceral mass; below, a muscular 
foot; while from either side a fold of the body-wall extends 
outwards and downwards as a mantle. Between the 

193 



194 SYSTEMATIC ZOOLOGY. 

mantle and the body and foot is a mantle-chamber or, since 
it frequently contains the gills (branchiae), it is frequently 
called the branchial chamber. 

The outer surface of the mantle and the dorsal part of 
the body frequently have the power of secreting a shell 
composed, chiefly, of carbonate of lime. This shell in 
some forms becomes split along the median line, so that 
two halves or valves result. In most other forms the shell 
becomes coiled into a spiral, and when this occurs the 
primitive symmetry becomes lost in part. 

Shells increase in size during the life of the animal. 
The mantle is continually laying down new layers of shell 
inside of those first formed, hence the older parts are 
thicker than the newer portions. Then the mantle is large]' 
when the new layers are secreted, so these project beyond 
the layers outside of them. As a consequence there occur 
on the outside lines of growth. 

In many species there are colored bands or spots upon 
the mantle, and these parts secrete carbonate of lime 
similarly colored, the result being that the shell is corre- 
spondingly striped or spotted. Again, in some, the edge 
of the mantle is produced into finger-like lobes, etc., and 
these cause spines and the like upon the shell. 

Shells are frequently spoken of as the houses or homes 
in which the animals live. As will be seen from the above, 
the shells are as much a part of the animal as is the cara- 
pax of a lobster or the coral of a coral polyp. The oyster 
or snail can never leave its shell. 

In most molluscs folds of the skin extend from the body- 
wall into the mantle-chamber. These are the branchm or 
gills. Inside of them are blood-vessels, and through their 
thin walls the blood is brought into close connection with 
the oxygen dissolved in the water. In the common ter- 



MOLLUSCS. 



195 



restrial molluscs gills are absent, but the inside of the 
mantle-chamber is lined with a fine network of blood- 
vessels, so that the whole organ resembles somewhat a 
lung, and has received that name. 

In the course of the blood there is a great difference 
between a mollusc and a fish. In the mollusc the blood 
returns at once from the gills to the heart, and is then 
forced by this organ to all parts of the body. The heart 
is situated in a chamber or pericardium * and consists 
of one or two (right and left) auricles which receive the 
blood, and a ventricle which pumps it to the body. In 
the squid and cuttlefish accessory or branchial hearts are 
added. These are placed at the bases of the gills and 
force the blood through these organs, from which it re- 
turns to the other or systemic heart, to go to all parts of 
the body. 

In all molluscs except the Acephala the region of the 
mouth is provided with a lingual ribbon (fig. 35, called 
also radula and odontophore) . 
This is a band of horny ma- 
terial, bearing on its free sur- 
face rows of hard and sharp 
teeth, so that the whole resem- 
bles a flexible file. It is sup- 
ported in such a way that it 
may be moved back and forth, 
thus rasping the food. In 
some gasteropods it can even 
be used in boring holes in the 
shells of other molluscs. This 
lingual ribbon is constantly growing at its deeper end, 
so that the loss by wear in front is continually made good. 

* This is the ccelom, greatly reduced in size. 




Fig. 35. — A bit of the lingual 
ribbon of a gasteropod 
(E burn a). After Cooke. 
Enlarged. 



196 SYSTEMATIC ZOOLOGY. 

The teeth on the ribbon vary in number and shape in 
different species. In some there are but three in a trans- 
verse row, while in others there may be over one hundred. 

In the ideal mollusc the alimentary canal goes straight 
through the body from mouth to vent. In nature it 
usually has some convolutions, increasing the amount of 
digestive surface. In the cephalopods and in most gas- 
teropods it becomes bent on itself, so that the vent is far 
in front, either upon the right side or even in the median 
line. In the gasteropods, when it is median, it is close to 
and dorsal to the mouth. In the cephalopods it is ventral. 
A large liver is always present. 

The nervous system (fig. 34, right) consists of at least 
three pairs of ganglia and the cords or commissures con- 
necting them, as well as the nerves going to the various 
parts. These ganglia are the cerebral, above the mouth; 
the pedal, primarily in the foot; and the visceral, farther 
back in the body. Both pedal and visceral ganglia are 
below the intestine; the pedal supplying the foot, the 
visceral the body and the mantle. To these three pairs 
others are frequently added. Sometimes the ganglia are 
widely separated, when the commissures are correspond- 
ingly lengthened; or they may be brought close together, 
with shortened connecting cords. 

Some molluscs lack organs of special sense ; others have 
eyes and ears. The ears are little sacs, usually near the 
pedal ganglion, but the eyes may have various positions. 
They may be on the sides of the head (squid), or on the 
sides or tips of tentacles arising from the head (snails), or 
scattered over the back (some slugs and chitons), or on 
the edges of the mantle (scallops), or on the end of the 
siphon (some clams). In some they are merely spots 
which have the power to distinguish between light and 



MOLLUSCS. 197 

darkness , and from these all degrees of development may 
be found to the extreme in the squid, where these organs 
are scarcely inferior to those of vertebrates in structure. 

For kidneys the molluscs have one or two organs 
(nephridia) consisting of convoluted tubes opening at their 
inner end into the pericardium and communicating with 
the exterior at the other. 

In some the sexes are separate; in others, like our 
land-snails, both sexes are united in the same individual. 
Molluscs reproduce exclusively by eggs, and in some there 
appears in development a trochophore-like larva which is 
regarded as indicating that these animals are related to 
the annelids (see p. 186). Molluscs are divided into five 
groups or classes : Amphineura, Gasteropoda, Scaphopoda, 
Acephala, and Cephalopoda. 

Class I.— AMPHINEURA. 

Setting aside a few rare forms 
this division is represented by the 
Chitons (fig. 36). These are dis- 
tinguished from other molluscs by 
many points of anatomy, while ex- 
ternally they may be recognized by 
having oval, flattened bodies covered 
above by a shell composed of eight 
transverse plates which overlap, from 
in front backwards, like the shingles fig. 36.— Chiton squamosus. 

» niJ , • . After Haller. 

on a roof. All the species are marine. 

Class II.— GASTEROPODA. 

The gasteropods receive their name from the fact that 
the foot usually forms a large sole or creeping disc extend- 
ing along the ventral side of the body. There is a distinct 




198 SYSTEMATIC ZOOLOGY. 

head, which usually bears sensory tentacles, and the eyes 
are commonly placed at the bases or on the tips of one 
pair of these structures. In some cases, as in most land- 
snails, these tentacles can be pulled back into the body 
in much the same way that one inverts the finger of a 
glove. 

In the majority of forms gills or branchice are developed 
in the mantle-chamber. In a few there is a pair of these 
organs, but in many one gill disappears, while in other 
species both true gills entirely disappear, and are either 
replaced by secondary gills developed on the back or in 
other regions; or the mantle-chamber may be richly lined 
with blood-vessels and thus be converted into an organ 
(lung) for breathing air. This is the case in all of our 
common land-snails. 

In all gasteropods a shell is present in the young, but in 
many it is lost before the animal becomes adult. It is 
never a bivalve structure, but is either conical, plate-like, 
or is coiled in a spiral. In some the spiral is flat, in others 
it may be elongate, and the turns may be either to the 
right or to the left, right-handed shells being in the great 
majority. In a large number of gasteropods a shell-like 
structure (operculum) is developed on the dorsal surface of 
the hinder part of the foot, and when the animal with- 
draws itself into the shell this operculum closes the open- 
ing like a door after all the soft parts are inside. 

Some of the peculiarities of the nervous system form the 
basis of the subdivision of the gasteropods. In one group 
(Euthyneura) the ganglia and the cords connecting them 
are much as in our diagram (fig. 34). In the other (Strep- 
toneura) the cords leading back from the brain become 
crossed so that the nerve which starts from the right side 
goes to a ganglion on the left, and vice versa. 



MOLLUSCS. 



199 



In all gasteropods a lingual ribbon (p. 195) is present, 
and this works against a plate or 'jaw' on the upper side 
of the mouth. The alimentary canal is rarely straight. 
Usually there are convolutions , and the whole is so bent 
upon itself that the vent is carried far forward, and may 
be placed upon the 'neck' just above the mouth. Some- 
times it, or the liver connected with it, becomes greatly 
branched. 



Subclass I. — Streptonettra. 

In these the nervous system is twisted; there is but a 
single pair of tentacles upon the head; and the gills are 
placed in front of the heart, a condition which leads many 
naturalists to call the group 'Prosobranchs.' 



Order I. — Diotocardia. 

In these forms the body retains 
its bilateral symmetry to a consider- 
able degree, and externally may ap- 
pear perfectly symmetrical. The name 
implies the existence of two auricles to 
the heart. In the limpets (fig. 37) 
the shell is a flattened cone; in the 
abalones it is somewhat ear-shaped 
and very weakly spiral, but in the top 
shells it is strongly spiral. The 
abalones alone have any economic 
value. Their shells, remarkable for 
having a series of holes in them, 
are composed of a greenish mother- 
of-pearl, which is extensively used in inlaid work. 




Fig. 37. — Limpet (Acmcea 
testudinalis). From Bin- 
ney's Gould. 



200 



SYSTEMATIC ZOOLOGY. 



Order II. — Monotocardia. 
Here belong the great majority of marine snails, all of 
which agree in having but a single gill and a single auricle 
to the heart. Few of them have any 
economic interest aside from those which 
feed upon oysters and other valuable 
shell-fish. These injurious forms — com- 
monly known as 'drills' — are able to 
bore holes through the shells of oysters, 
etc., by means of their lingual ribbons. 
Many, however, are great favorites with 
collectors, among them the strombs 
(fig. 38), cones, cowries, and olives. 
Some of the cones are noticeable from 
the fact that they have a poison-gland 
connected with the lingual ribbon. Some species, for- 
merly grouped as a distinct order of Heteropoda, are espe- 
cially modified for a life on the high seas. 
Subclass II. — Euthyneura. 
In the Euthyneura the nervous system is without a 
twist, and the head almost always bears two pairs of 
tentacles. 

Order I. — Opisthobranchia. 

These forms are all marine, and have but two divisions 
to the heart — an auricle and a ventricle, the latter being in 




Fig. 38. — S t r o m b 
(S trombus pugilis). 
After Woodward. 




Fig. 39.— Naked mollusc (Doris), showing the gills, above to the right. 

front of the former. Some are provided with a spiral 
shell, while others 



called Nudibranchs or naked mol- 



MOLLUSCS. 



201 



luscs (fig. 39) — are without such protection in the adult, 
although shells are present in the young. In the nudi- 
branchs there are commonly developed gills upon the dor- 
sal surface, and in the living condition these forms are, 
from their bright colors, among the most attractive of 
molluscs. Here, too, are forms (Pteropods) especially de- 
veloped for a life on the surface of the ocean, the foot 
being modified into a pair of wing-like structures. 



Order II. — Pulmonata. 

The great majority of the land- and 
fresh-water snails and slugs belong 
here. In them gills have disap- 
peared, and the mantle-cavity has 
been modified into an organ (lung) 
for breathing air, the opening to 
which is to be seen on the right 
side of the body. Over six thousand 
species belong here, some (snails) 
having a well-developed spiral shell, 
while the slugs (fig. 40) are appar- 
ently shell-less; but in these slugs 
one can frequently find a rudimen- 
tary shell imbedded in the mantle. 

Class III.— SCAPHOPODA 
(Tooth-shells). 




Fig. 40. — Slug (Lima* 
campestris). s, respir- 
atory opening. From 
Ludwig's Leunis. 



In these the mantle edges are fused 
below, forming a tube, and as a result 
there is formed a tubular shell, open 
at both ends, in shape something like the tusk of an 
elephant. The foot is relatively large, and is adapted for 
digging in the sand in which these animals live. There 
is no distinct head, but the mouth is provided with a 



202 SYSTEMATIC ZOOLOGY. 

lingual ribbon. In the anterior part of the mantle- 
cavity are a pair of bunches of long threads of unknown 
function; possibly they are sensory, possibly respiratory, 
in nature. All of the tooth-shells are marine. 

Class IV.— ACEPHALA. 

In the Acephala, as the name implies, there is no dis- 
tinct head. The body is flattened from side to side, and 
the two sides are almost exact repetitions of each other. 
On either side of the body there is a strong outgrowth of 
the body-wall, the mantle, which secretes on its outer sur- 
face the shell, which is divided in the median line so that 
two halves or valves result. Between the mantle folds 
and the body is the mantle-chamber, and into this on 
either side there usually hangs down a pair of leaf-like 
gills,* whence the name Lamellibranchs, often applied 
to the class. The muscular foot projects from the lower 
surface of the body. With these features the animal 
presents a marked resemblance to a book in which the 
valves represent the covers; the mantle, gills, body, and 
foot, seven leaves. 

Where the two valves are hinged together there is an 
elastic ligament which tends constantly to open the 
valves, which are closed by means of adductor muscles 
extending from one valve to the other. Usually there are 
two of these muscles — anterior and posterior — but the 
anterior of these may disappear. 

In some, as in the oyster, the mantle edges are free from 
each other throughout their extent; but not infrequently 
they become fused in places, leaving openings between. 
At the posterior end this fusion frequently results in the 
formation of two tubes or siphons connecting the mantle- 

* It is not necessary here to include the gill features of Cuspi- 
daria, Silenia, etc. 



MOLLUSCS. 



203 



cavity with the outer world (fig. 41). In some these 
siphons may be greatly developed as long tubes and 




Fig. 41. — Quahog ( Venus mercenaria), with foot and siphons extended. 

then strong retractor muscles to draw them back are 
present. All of these muscles — adductors, retractors, etc. 
— leave their impress on 
the shell, so that the 
student, with the shell 
alone, may know of some 
of the structures of the soft 
parts (fig. 42). 

Water is drawn into the 
mantle-cavity by means 
of very minute hair-like 
structures (cilia) which 
cover the gills and other 
parts. These cilia are in constant motion,* and thus 
currents of water are produced, flowing always in one 

* The teacher should demonstrate this ciliary actipri Vffict^r the 
compound microscope, 




Fig. 42. — Inside of bivalve shell show- 
ing muscular impressions of a, an- 
terior adductor; p, posterior adduc- 
tor; s, siphonal muscle. 



204 SYSTEMATIC ZOOLOGY. 

direction. This water brings oxygen to the gills and, 
through them, to the blood. It also brings minute 
animals and plants. These are passed on to the labial 
palpi, fleshy folds, near the mouth /"which are similarly 
ciliated, and from these organs the cilia force the food 
into the mouth. 

In the nervous system we always find cerebral, pedal, 
and visceral ganglia, and frequently parietal ganglia 
between the cerebral and the visceral, the first being 
above, the others beside or below, the alimentary canal. 
Ears are present, connected with the pedal ganglia; and 
eyes may be present, either upon the edges of the mantle 
or at the tips of the siphons. 

The alimentary canal is always provided with stomach 
and liver. Connected with the stomach a blind sac fre- 
quently occurs, and in this there may be a peculiar trans- 
parent rod, the crystalline style, of uncertain use. The 
intestine goes from the stomach first towards the foot, 
then mounts towards the hinge-line, and frequently passes 
through the ventricle of the heart. 

The heart consists of a single ventricle and usually two 
auricles, but sometimes there is but one of the latter. 
The heart is situated in a chamber (pericardium), which 
is connected with the exterior by means of a pair of con- 
voluted kidney tubules or nephridia (organ of Bojanus). 

A thoroughly satisfactory classification of the Acephala 
has not yet been worked out. Possibly the best is that 
based upon the structure of the gills, but a more convenient 
one for our purposes is based upon the presence or absence 
of a siphon. 

Order I. — Asiphonida. 

The edges of the mantle free; no siphon present. Most 
prominent of this order are the oysters, These are all 



MOLLUSCS. 



205 



marine, species being found in all but the colder seas. 
In these forms the animals lie upon one side, and there 
results an inequality of the valves. On our east coasts 
oysters extend from the Gulf of Mexico to Cape Cod. 
Further north (except in the Gulf of St. Lawrence) they 
are not found native, but are 'planted.' The centre of 
the oyster industry is Baltimore. In 1894 the oyster- 
fishery of the United States amounted to over $16,000,000. 
In the scallops (fig. 43) the shell is fluted, and the 




Fig. 43. — Scallop (Pecten irraddans). From Binney's Gould. 

valves may be unequal or similar in shape. These mol- 
luscs can swim freely by rapidly opening and closing the 
valves of the shell; and they are further noticeable from 
the fact that around the edge of the mantle are a series of 
rather complicated eyes. The 'scallops' of the markets 
are the adductor muscles of these molluscs. In the pearl- 
oysters the inner layer of the shell has a pearly appear- 
ance, and these forms also produce, like some other mol- 



206 SYSTEMATIC ZOOLOGY. 

luscs, the precious pearls. These pearls are really the 
shell-forming secretions of the mollusc around some 
foreign body and they receive their beauty from the way 
in which the shell is deposited around the centre. Fresh- 
water mussels, to be referred to a few lines below, also 
form pearls of value. The shell of the pearl-oyster also 
has its value, for it furnishes the mother-of-pearl used 
for buttons, knife-handles, for inlaying, etc. The pearl- 
oysters occur in the Indian Ocean, and also in the Bay 
of Panama. 

The salt-water mussels (fig. 44) so abundant on the 




Fig. 44. — Salt-water mussel (Mytilus edulis). 

mud flats all along northern shores have a peculiar gland 
in the foot which secretes strong silky threads (byssus) by 
which these animals anchor themselves. The common 
species, which occurs both in Europe and New England, 
is called the edible mussel; but not infrequently severe 
sickness follows its use as food. The fresh-water mussels 
or Unios are especially abundant in America, the Mis- 
sissippi basin being their centre. They are useless as 
food, owing to their strong taste. There are possibly a 
hundred species of these forms in America; over six 
hundred so-called species have been described. In their 
siphonal structure they form a transition to the next 
group. 



MOLLUSCS. 



207 



ORDEE II. SlPHONATA. 

In these the margins of the mantle have grown together 
posteriorly into a double tube or siphon, and accordingly 
as this siphon is developed the 
animal can burrow below the 
surface and still obtain its nec- 
essary supplies of water and 
food; for these tubes can 
reach the surface, and through 
them there is a continual flow 
of water — inward through the 
ventral, outwards through the 
dorsal, passage (fig. 45). 

The great majority of bi- 
valve molluscs belong here, but 
there are comparatively few of 
general interest. The largest 
of all clams, the giant clam 
of the East Indies, with shell 
sometimes weighing over 300 
pounds, belongs here, as do the 
quahog and the long clam, 
which are used as food. One 
of these forms, the Teredo or 
ship-worm, is a serious pest, 
as it bores in wood, destroying 
the piles of wharves, the bot- 
toms of boats, etc. Their bur- 
rows run to long distances, but 
all their food and water must 
be drawn in through the si- 
phons, One great inundation in Holland at the begin- 




Fig. 45. — Long clam (Mya are- 
naria) buried in the mud. The 
arrows show the currents in 
the siphons. 



208 SYSTEMATIC ZOOLOGY. 

ning of the last century was directly due to the borings of 
these forms. 



Class V.— CEPHALOPODA (Squid and Cuttlefish). 

The Cephalopods derive their name from the fact that 
the circle of tentacles or arms around the mouth (i.e., on 
the head) was compared to the foot of other molluscs. 
Later investigations show that these tentacles represent 
but a part of the foot, the siphon also belonging to the 
same category. These same arms, which are either eight 
or ten in number, bear sucking organs by means of which 
these animals hold fast their prey. In the pearly nautilus 
only are the arms lacking, and here they are replaced by 
about a hundred smaller organs. 

The head, which is separated from the body by a distinct 
neck, bears a pair of eyes — simple in the nautilus, but al- 
most as complex as those of man in the other forms. In 
these more highly developed eyes there are retina, lens, iris, 
cornea, and cavities resembling those occupied by the 
aqueous and vitreous humors (see Vertebrates). Yet the 
resemblances are superficial; the structures are in reality 
totally different. 

The mantle is connected with the body in the region of 
the so-called back. Below, it encloses a good-sized mantle- 
cavity, open in front. It is very muscular, and the open- 
ing about the neck can be closed at will, so that the only 
connection between the mantle-chamber and the outside 
world is through the tube of the siphon. This is a tubular 
structure on the ventral surface, in no way homologous 
with the similarly named tubes of the Acephala. If one 
of these animals fill its mantle with water, close the neck 
opening, and then force out the water by contracting the 



MOLLUSCS. 209 

mantle ; the water will stream from the siphon in a strong 
jet, which by its reaction forces the animal in the other 
direction. This apparatus forms with many, and especially 
with the squid, the chief organ of locomotion, and in these 
the tip of the siphon can be bent in any direction, so that 
the animal may go forwards, backwards, etc., according 
as it wishes. 

In the mantle-cavity are one or two {Nautilus) pairs of 
feather-like gills, and into the same chamber empty the 
ducts of the kidneys and reproductive organs, as well as 
the intestine, and the ink-sac connected with it. This 
last organ secretes a dark-colored fluid, which when dis- 
charged into the water makes a cloud, and thus the animal 
is enabled to escape unseen. From this ink the pigment 
sepia and some kinds of India ink are manufactured. 

Imbedded in the skin of the mantle are pigment spots or 
chromatophores , which are interesting from the fact that 
they can be enlarged or contracted by the nervous system. 
When enlarged they nearly touch each other, and thus give 
the body their general hue (red). When contracted they 
appear as minute black points, while the general body 
color (translucent white) then prevails. As a result we 
have in these animals a power of color-change far more 
striking than that of the chamseleons. 

Most living cephalopods have no external shell. Inside 
of the back, however, is a shell — the pen — which may be 
either feather-shaped and horny, or broader, thicker, and 
calcareous. In this last condition it furnishes the 'cuttle- 
bone' so often given to cage-birds. The paper-nautilus 
has a shell which is formed only by the female; it is se- 
creted, not by the mantle, but by one pair of the arms, 
and this shell is really a protection for the eggs. In the 
pearly nautilus, on the other hand, there is a true shell, 



210 SYSTEMATIC ZOOLOGY. 

which is coiled in a spiral and is divided by partitions 
into a series of chambers, only the outer one being occu- 
pied by the animal (fig. 46). Similarly chambered shells 
are very abundant among fossils. 

The mouth is armed with a pair of horny jaws shaped 
much like those of a parrot. These are very efficient in 
biting food; but any morsels taken into the mouth are 
subjected to further subdivision by means of the lingual 
ribbon, which is, as its name implies, a ribbon-like mem- 
brane, bearing on its surface numbers of minute teeth, 
which rasp the food into fine shreds. 

The heart is situated in a pericardium and is systemic; 
that is, it pumps the blood returning from the gills to the 
various parts of the body. A peculiarity of the circulatory 
system is that in all, except the pearly nautilus, the vessel 
carrying blood to the gills develops a special pumping 
organ, the branchial heart. 

The various ganglia of the nervous system are (except 
the stellate ganglia) placed close together in the head, and 
from this centre nerves radiate to all parts of the body, 
those going to the tentacles being connected with each 
other by a circular cord. The stellate ganglia, of which 
there are two, are upon the anterior part of the mantle. 
The nerves which radiate from them control the motions 
of the mantle. 

The cephalopods are all marine. They are carnivorous, 
feeding upon fishes, etc., which they capture with their 
arms and hold fast by their numerous suckers. The 
larger forms might be no mean antagonist for man; but 
the monster described by Victor Hugo is without counter- 
part in nature. The cephalopods are divided into two 
orders, according to the number of gills. 



MOLLUSCS. 



211 



Order I. — Tetrabranchiata. 

In the Tetrabranchs there are two pairs of gills (i.e., four 
in all); the head bears numerous short tentacles without 
suckers, and the body is enclosed in a chambered shell. 
The pearly nautilus is the only living representative of this 




Fig. 46. — Female Nautilus, the shell laid open (from Ludwig's Leunis). 1, man- 
tle; 2, dorsal lobes; 3, tentacles; 4, head fold; 5, eye; 6, siphon; 8, shell 
muscle; 9, living-chamber; 10, partitions between chambers; 11, siphuncle. 

group. It occurs in the East Indian seas, and, while the 
shells are very common, the animal is very rare in museums. 
In geological times allied forms were very abundant, and 
are known as Ammonites (with tightly coiled shells), and 
Orthoceratites (with straight shells), etc. 



Order II. — Dibranchiata. 

These have two gills (one pair), and long, sucker-bearing 
arms. An ink-sac is always present. The order is sub- 
divided into the Octopoda, in which there are eight arms 
(fig. 47), and the Decapoda, in which the number is 
increased to ten by the addition of a pair of longer arms. 
In the Octopoda there is no internal shell, and the body 



212 SYSTEMATIC ZOOLOGY. 

is saccular. Here belong the octopus, poulpes, etc., as 
well as the paper nautilus, which does not sail with its 
shell as a boat, and its broadened arms erect to catch the 
wind, as it is often said to do. The Decapoda include the 
squid, the sepia, and other forms. The smaller squid 




Fig. 47. — Octopus bairdii. From Verrill. One arm on the right side is modi- 
fied for purposes of reproduction. 

are abundant, and are caught in large numbers for bait 
in fishing for cod. Near Newfoundland, and in other 
parts of the world, giant squid are occasionally found, 
the largest one known having a body length of twenty feet. 
The length of the arms was not mentioned in the account. 

Summary of Important Facts. 

1. The MOLLUSCA receive their name from the soft 
nature of the body, in which the body-cavity is greatly 
reduced. 

2. They have a body from which a foot depends below 



MOLLUSCS. 213 

and a fleshy mantle fold on either side, enclosing a pair of 
branchial chambers between mantle and foot. 

3. The mantle usually secretes a shell which increases 
in size during life, the stages of increase being shown by 
lines of growth. 

4. The true branchiae project into the branchial chamber; 
they may be lost and replaced by other gills developed 
from other parts of the body. 

5. A characteristic feature of all except the Acephala 
is the lingual ribbon. 

6. The nervous system consists of at least three pairs 
of ganglia connected by nervous cords. 

7. The reproduction is exclusively by eggs. A trocho- 
phore may occur in development. 

8. The Mollusca are divided into Amphineura, Gastero- 
poda, Scaphopoda, Acephala, and Cephalopoda. 

9. The Amphineura have a very simple nervous sys- 
tem. In the Chitons, which belong here, there are eight 
plates of shell on the back. 

10. The Gasteropoda have a distinct head with ten- 
tacles and a creeping foot. 

11. The shell is unpaired, more or less conical, and fre- 
quently spirally coiled. It is occasionally lacking in the 
adult. 

12. The Gasteropoda include the Diotocardia, Mono- 
tocardia, Opisthobranchia, and Pulmonata. 

13. The Scaphopoda are primitive forms with tubular 
shell and no distinct head. 

14. The Acephala lack head and lingual ribbon, and 
have a bivalve shell. 

15. The edges of the two mantles may unite behind to 
form the siphon. 

16. The foot is fleshy and more or less hatchet-shaped. 



214 SYSTEMATIC ZOOLOGY. 

17. The Acephala may be divided into Asiphonida and 
Siphonata. 

18. The Cephalopoda have no true foot, this being 
represented by the siphon and the tentacles around the 
mouth. 

19. The shell, when present, is unpaired. When present 
it may be external or internal. 

20. The ink-sac is peculiar to Cephalopoda. 

21. The eyes are usually highly organized, and resemble 
those of vertebrates. 

22. There are present special branchial hearts to force 
the blood to the gills, and a systemic heart to force it 
through the body. 

23. The Cephalopoda are divided into Dibranchiata and 
Tetrabranchiata according to the number of gills. 



Phylum V.— ARTHROPODA. 

The word Arthropoda means 'jointed foot/ and is very 
characteristic of all that immense series of forms which, 
like the grasshopper and the crayfish, have an external 
skeleton which only permits of motion by a thinning or 
jointing at intervals. In this way both body and limbs 
have this jointed appearance, but with the body this joint- 
ing or segmentation of the external surface is associated 
with features of internal structure which must have a 
moment's attention. This external jointing of the body 
divides it into a series of essentially similar rings, somites, 
or metameres, and in each of these we find parts of all the 
internal organs. That is, the segmentation is not con- 
fined to the external surface, but is characteristic of all 
parts. 

In an ideal arthropod each of these segments would be 
an exact repetition of its fellows, much as they are in 
the annelids (p. 183), but in nature we find that certain 
segments or parts of certain segments become over-devel- 
oped (hypertrophied) , and this produces an under-develop- 
ment (tendency towards atrophy) in others. Thus every 
segment in our ideal arthropod would bear a pair of 
jointed appendages, but these are frequently atrophied 
on some of the segments. Again, there is a tendency in 
some regions, and especially in the head, for a more or 
less complete fusion of segments, so that the number can 

215 



216 SYSTEMATIC ZOOLOGY. 

only be ascertained by the appendages or by the features 
presented in development. 

Usually these segments can be grouped in regions, of 
which, at most, three can be distinguished: in front the 
head; next^ the thorax; and behind, -the abdomen (fig. 
48). The head is largely concerned in the taking of food, 




Pig. 48s — Diagram of grasshopper showing the body divided into the three 
regions: head, thorax, and abdomen. 

and is usually the seat of the special senses. The thorax 
is the locomotor region, while in the abdomen the primi- 
tive segmentation is most marked. 

Through the body as an axis runs the alimentary canal, 
the mouth being on the under surface of the head, while 
the vent is at the tip of the abdomen. Above the diges- 
tive tract lies the heart, which in many forms has a 
chamber in each of several somites of the body; that is, 
the heart is segmented. On the floor of the body, below 
the alimentary canal, is the nervous system, which ex- 
hibits this segmentation in a more marked degree. In 
each segment there is a paired enlargement or ganglion 
from which nerves go to the various organs of the seg- 
ment. These ganglia of the successive segments are con- 
nected with each other by a double nerve-cord, so that 
all are in communication with each other. At the front 
end of the body one of these nerve-cords passes on one 
side of the oesophagus, the other on the other, and above 
it they unite with a large compound ganglion, the so- 
called brain. In this way a part of the nervous system 



ARTHROPODS. 217 

is brought above the alimentary canal, while the rest 
lies below. In other words, the digestive tract passes 
through the nervous system, a condition which is common 
in the non-vertebrate animals, the structure in the arthro- 
pods closely paralleling that in the annelids. 

Two kinds of eyes occur in the Arthropoda, the simple 
or ocelli and the compound, each with an apparatus 
(lens) to concentrate the light and a retina for its recog- 
nition. As the name implies, the compound eye consists 
of a number of simple eyes closely united together, the 
whole forming a visual apparatus, each element of which 
sees a part of the object, the whole visual impression 
thus resembling a mosaic. 

The organs of respiration are never connected with the 
alimentary canal, but are always developments of the 
surface (ectoderm) of the body. They are of two kinds: 
gills or branchiae in aquatic forms and tracheae or air- 
tubes in the forms which do not live in the water. Gills in 
the arthropods are outgrowths of the body-wall, usually 
much folded or divided to afford additional surface, and 
in these are blood-vessels. In the case of gills, then, we 
may say that the blood is brought to the oxygen dissolved 
in the water for that exchange of gases (carbon dioxide 
and oxygen) upon which respiration depends. With 
tracheae, on the other hand, the respiratory surface is 
obtained by a forcing of the external surface into the 
deeper parts, much as one might invert the finger of a 
glove into the palmar region. In the tubes thus formed 
air can enter, and thus the oxygen is brought to the 
blood and other tissues of the body. It is interesting to 
note that the more the tracheae are developed, the more 
the circulatory organs are reduced. The ' lungs ' of the 
arachnid are to be regarded as modified gills. 



218 SYSTEMATIC ZOOLOGY. 

The excretory organs of the arthropod are formed upon 
two plans. In the one (Crustacea and Acerata) we have 
a few organs, like the green gland and the shell gland, 
which are apparently to be regarded as comparable to 
the nephridia of the annelids (p. 184). The other type ; 
the Malpighian tubes (Arachnida and Insecta) are con- 
nected with the alimentary tract. 

The Arthropoda are by far the largest group of animals, 
the number of forms living to-day being estimated from 
half a million to a million or more. 

The Arthropoda are subdivided into three groups 01 
classes: Crustacea, Acerata, and Insecta, and besides 
these a few forms of uncertain position. 

Class I.— CRUSTACEA. 

The crayfish and sow-bug may be taken as types of the 
Crustacea, or crab-like forms. All have two pairs of 
appendages (antennae) in front of the mouth; they have 
a varying number of segments at the front of the body, 
covered by a common shell or carapax, and, excepting 
gill-less microscopic forms, they all breathe by means of 
gills attached to some of the feet. 

The number of segments in the body varies; in the higher 
groups it is constantly twenty, but in the lower it may fall 
far short of, or far exceed, that number. The regions also 
vary in extent and cannot be compared throughout the 
group. Taking the segments connected with the senses 
and with eating as constituting the head, this region may 
contain as few as five or as many as eight segments. Not 
infrequently the head and the next region of the body are 
united so that they are called a cephalothorax. The abdo- 
men is usually well developed, but it may be reduced to a 



CRUSTACEA. 219 

mere stump, as in the barnacles. Any of the segments 
except the last one may bear appendages. The append- 
ages most commonly present are the two pairs of antennae 
in front of the mouth, next those concerned in eating and 
grouped as 'mouth -parts.' Of these there are always a 
pair of biting-jaws or mandibles, then two pairs of acces- 
sory jaws or maxilla?, and lastly a varying number of 
'jaw-feet' or maxiliipeds. Behind these there may be the 
walking-feet upon the thorax and the swimming-feet upon, 
the abdomen. 

If these appendages be studied in the adult of some 
species or in the young of all, they are found each to con- 
sist of a basal joint, bearing two jointed branches, the 
exopod and endopod. With growth of the animal the 
exopod frequently disappears. 

The gills by which most Crustacea breathe are thin out- 
growths of the body, usually closely connected with some 
of the appendages, either of the thorax or of the abdomen. 
In shape they may be plates or plumes or sacs, but all are 
traversed by blood-vessels so that the blood is brought in 
close proximity to the water. In some cases these gills 
hang freely into the water, in others they are placed in 
special gill-chambers, and then there is an arrangement 
of parts for pumping fresh water over them. In the ter- 
restrial Crustacea these gills still serve as breathing- 
organs, as in the sow-bugs, and are constantly kept moist. 
In some of the lower Crustacea there are no special organs 
of respiration, the thin walls of the body affording suffi- 
cient surface for the purpose. 

The alimentary canal is nearly straight, and there is 
usually a chewing -stomach in which the food is ground 
by hard teeth in the walls, and beyond this there is fre- 
quently a straining-stomach. A large so-called liver is 



220 SYSTEMATIC ZOOLOGY. 

always present, pouring digestive juices into the alimentary 
canal behind the stomach. The eyes are either simple or 
compound. In the simple eyes there is a single lens for 
the whole structure, while the compound eyes are com- 
posed of many separate eyes, each with its own lens. In 
some cases the compound eyes are placed on jointed 
stalks, at others they are on the walls of the head. Ears 
have been found in some forms. Usually they are sacs 
in the base of the antennulae, but in the opossum-shrimps 
they occur near the end of the abdomen. The hairs which 
occur over the body are organs of touch, and probably 
some of them around the mouth and on the antennae 
serve as organs of taste and smell as well. 

A heart is lacking in a few forms. When present it is 
dorsal in position, but may be either in thorax or abdo- 
men. It may be a long tube with several chambers, or 
a short thick muscular organ without divisions. The 
blood returning from the gills enters the heart and is 
forced thence to all parts of the body, a condition quite 
different from what is found in the fish. It does not 
flow throughout its course in closed vessels, but escapes 
from them and comes into large spaces (lacuna?) between 
the various organs and muscles, and from the largest of 
these lacunae, near the floor of the body, it again goes to 
the gills. 

In the Crustacea the excretory organs (nephridia) open 
to the exterior entirely independently of the alimentary 
canal. In the higher Crustacea (crayfish, etc.) these 
nephridia are known as 'green glands' and open at the 
base of the antennae (second segment of the body); in 
the lower Crustacea they are called 'shell-glands' and 
open at the base of the second maxillae (fifth segment). 

The sexes are separate in all except the barnacles, and 



CRUSTACEA. 



221 




the ducts of the reproductive organs open to the exterior 
in the thoracic region, never 
in the abdomen. In almost 
all forms the eggs are carried 
about by the mother until they 
are hatched. In almost all 
the lower Crustacea the young 
escapes from the egg in a very 
immature condition, known as 
a Nauplius (fig. 49), a name 
given years ago under the be- 
lief that it was an adult. The 
nauplius has an unsegmented 
body, a single median eye, and 
only three pairs of appendages 
— antennulse, antennae, and 
mandibles — the antennulse being solely sensory, while 
antennae and mandibles are used in 'both swimming and 
eating. In the higher Crustacea the nauplius stage is 
passed in the egg, and the young hatches in a more ad- 
vanced condition — sometimes closely like the adult in all 
except size. Growth is allowed for by frequent molts 
of the external cuticle of the body. 

Over 10,000 species of Crustacea are known, almost all 
of them aquatic, and the majority marine. Only a few, 
like the sow-bugs and land-crabs, live on the land. A few 
are vegetarians, some are parasites on other animals, but 
the majority are scavengers, feeding on decaying organic 
matter. The Crustacea may be conveniently divided into 
two subclasses: Malacostraca and Entomostraca. 



Fig. 49. — Nauplius stage of fairy- 
shrimp (Branchipus). After 
Claus. 



222 SYSTEMATIC ZOOLOGY, 

Subclass I. — Entomostraca. 

This division contains a large number of forms, mostly 
small, or even microscopic in size. The number of body- 
segments is usually less than twenty, but occasionally 
there may be many more. Some are decidedly shrimp- 
like in form, but with others parasitic habits have resulted 
in such changes that there is little external resemblance 
to a crayfish or a crab. 

The Entomostraca include the Phyllopoda, Copepoda, 
Ostracoda, and Cirripedia. 

Order I. — Phyllopoda. 

These, the lowest of the Crustacea, receive their name 
from the leaf-like character of the thoracic feet. Some, 
like Branchipus, are shrimp-like in appearance; others 
(Apus) have a broad shield over a part of the body, while 
still others have the body enclosed in a bivalve shell, 
much like that of a clam. Most of the species inhabit 
fresh water; a few live in brine. Branchipus, the fairy- 
shrimp, is common in snow-pools in the northern states. 
Its eggs require to be dried by the summer sun before 
they will develop. 

Order II. — Copepoda. 

The Copepoda include two groups of forms. The one 
includes both fresh and salt-water forms of regular crus- 
tacean appearance (fig. 50), while the other contains 
forms, commonly known as fish-lice, which are parasitic 
on fishes, and which as a result have in some cases degen- 
erated to such an extent that, without a knowledge of 
their history, one would hardly suspect them of being 
crustaceans were it not for their young. In their history 



CRUSTACEA. 



223 



they pass through a free-swimming nauplius stage, then 
attach themselves to a fish, after which the retrogression 




Fig. 50. — A Copepod (Cyclops). From Hertwig. 

sets in. It is noticeable that the female becomes much 
more degenerate than the male. 



224 



SYSTEMATIC ZOOLOGY. 



Order III. — Ostracoda. 

These forms are enclosed in a 
firm bivalve shell into which all 
parts can be retracted and the 
valves closed like those of an 
oyster or clam. These forms are 
"laS^iftTr small, only a fraction of an inch 
in length. They abound in the 
bottoms of fresh-water ponds and in brackish water. 




Fig. 51 

ostracode, en 
Turner, 



Order IV. — Cirripedia (Barnacles). 

In the Barnacles the body is usually enclosed in a 
calcareous shell composed of a number of parts, the shell 
being directly attached to some 
solid support, as in the acorn bar- 
nacles so common on the rocks at the 
shore, or there is a fleshy stalk, as 
in the goose - barnacles (fig. 52). 
At one place the shell gapes and 
from this opening the six pairs of 
two-branched feet are protruded with 
a sweeping motion. These feet are 
finely haired and the interlacing 
hairs make a fine net which strains 
minute forms from the water and 
carries them to the mouth inside the shell. The calcare- 
ous shells caused the barnacles to be regarded as molluscs 
for a long time, but the nauplius stage in development, 
the two-branched jointed feet, and other features pro- 
claim them truly crustacean. 




Fig. 52. — Goose - barna- 
cles (Lepas anatifera). 
After Schmarda. 



Mention should be made here of a large group of extinct 



CRUSTACEA. 



225 



animals, the Trilobites (fig. 53), which recent investiga- 
tions have shown to be 
crustaceans, but which can- 
not be more definitely 
placed within that group. 
They agree with neither 
Entomostraca nor Malacos- 
traca in their structure. 
They have a flattened body, 
in which head, thorax, and 
abdomen are readily dis- 
tinguished, and in which 
both thorax and abdomen 
consist of an axial portion, 
and two lateral regions or 
lobes, whence the name of 
the group. The head bears 
a pair of compound eyes, 
a single pair of antennae, 
and four pairs of append- 
ages, which served at once for walking and for taking 
food. Each segment of thorax and abdomen supports a 
pair of two-branched appendages. Trilobites appear in 
the earliest fossil-bearing rocks, and the group died out 
soon after the period of coal-formation (in the Permian). 




Fig. 53. — Restoration of the under 
surface of a Trilobite, showing the 
appendages. After Beecher. 



Subclass II. — Malacostraca. 

This group contains the larger and higher Crustacea, in 
which the body consists of twenty somites,* all of which 
except the last (telsori) may bear appendages. Com- 
pound eyes are usually present; and the nauplius stage 
* Twenty-one in Nebalia. 



226 SYSTEMATIC ZOOLOGY. 

(p. 221) is usually passed in the egg. Besides several 
unimportant groups, this subclass contains the orders 
Decapoda and Tetradecapoda. 

Order I. — Decapoda. 

Those forms which are commonly known as crayfish, 
shrimps, lobsters, prawns, and crabs are collectively 
known as Decapods, from the fact that, including the 
large claws, they have ten walking-feet. Besides they all 
have eyes on movable stalks, the anterior part of the 
body or cephalothorax (thirteen segments) is covered by 
a fold of the integument known as the carapax, and the 
gills are (usually) borne packed away in a pair of gill- 
chambers beneath the carapax above the walking-legs. 

This group of Decapoda is subdivided into three sub- 
orders, according among other things, to the characters 
presented by the abdomen. In the Macrura it is, as 
shown in the crayfish, very large, and is carried well 
extended; in the Brachyura it is much smaller, not 
nearly so large as the cephalothorax, and is folded up 
beneath the latter region so that it is not visible from 
above. In the third group, the Anomura, the abdomen 
is intermediate between the conditions found in the other 
groups, and frequently it is much softer than the other 
regions. 

Of the Macrura the most important are the lobsters, 
which are large marine forms differing in a few points, 
except size, from the fresh-water crayfish. These play 
a great part in the food-supply of northern Europe and 
the eastern United States. They are mostly captured 
by sinking large wooden traps (lobster-pots) baited with 
refuse fish, and at intervals hauling up the pots. The 



CRUSTACEA. 



227 



number thus taken upon the shores of New England and 
Canada amounts to between twenty and thirty million 
annually. Overfishing is, 
however, rapidly reducing 
the numbers caught. Cray- 
fish are used largely as 
food in Europe, and are 
bred in ponds for the mar- 
ket, but in America they 
are largely neglected. 
Shrimps and prawns are 
mostly salt-water forms, but 
some of the prawns occur in 
fresh water in the warmer 
parts of the world. The 
line between the two is not 
easily drawn except by say- 
ing that the body of the 
shrimp (fig. 54) is flat- 
tened (depressed) from 
above downwards, while 
that of the prawn is com- 
pressed (flattened from side 
to side). In America, _, _ 

' 7 Fig. 54. — Common shrimp (Crangon 

' Shrimp Salad ' is almost vulgaris). From Emerton. 

universally made from prawns. 

Of the Anomura, the most interesting are the so-called 
hermit-crabs (fig. 55). These are somewhat lobster-like, 
but the abdomen is but slightly hardened, and so, to 
protect this vulnerable part of the body, the crab inserts 
it in a deserted snail-shell, and this ' house' he carries 
about with him wherever he goes, retreating into it and 
closing the opening at the approach of danger with his 




228 



SYSTEMATIC ZOOLOGY. 



solid pincing-claws. With increase in size the crab must 
move into a larger shell. In other Anomura the back is 
soft, and these 'false hermits' carry half a clam-shell 
about with them to cover their weak point. 

Only a few of the true crabs or Brachyura live in fresh 
water. In the tropical and semi-tropical regions are 




Fig. 55. — Hermit-crab (Eupagurus bernhardus) in a snail-shell. From Emerton. 

those which live on the land; but the great majority — a 
thousand different species — live in the sea. The larger 
species have some economic value as food, but all of them 
are important as scavengers. In America ' soft-shelled 
crabs ' are prominent in our markets at the proper season 
of the year. During the rest of the time this crab, known 
as the 'blue crab' (Neptunus hastatus), has as hard a 
shell as any crab, but when the proper moment comes 
the shell splits across the hinder margin, and out from 
this opening comes the body covered only with the thin- 
nest skin, and at this time alone it is a soft 'shell/ All 



CRUSTACEA. 



229 



other Crustacea molt or shed their skin in the same way, 
the new skin rapidly growing hard again, but the blue 




Fig. 56. — Shore-crab (Cancer irroratus). 

crab is the only one taken in sufficient abundance at this 
time to be of economic importance. 



Order II. — Tetradecapoda. 

Contrasted to the Decapods are the fourteen-footed or 
tetradecapodous forms, of which the sow-bug is one type. 
In these we can distinguish clearly head, thorax, and 
abdomen, the joints of the thorax being freely movable 
on each other. The eyes are not placed upon movable 
stalks, but are scarcely elevated above the general sur- 
face of the head. Most of these forms are marine; a 
few live in fresh water, and still fewer, like the sow-bugs 
and pill-bugs, upon the land. All are small, those which 
reach two inches in length being the veritable giants 
among the group.* 

* An isopod from the greater depths of the ocean reaches a length 
of six inches. 



230 



SYSTEMATIC ZOOLOGY. 



There are two subdivisions of Tetradecapods: Isopoda 
and Amphipoda. 

In- the Isopods (fig. 57) the 
body is depressed, as in the 
sow-bug, and the gills are borne 
under the abdomen. Most of 
the Isopoda feed upon decay- 
ing matter, but some have 
become parasites upon other 
animals, and have consequently 
so changed their appearance 
that one knowing only the 
adult would never regard them 
as Isopods at all. But the young 
settle the question, since before 
they begin their parasitic life 
they are regular Isopods. 

In the Amphipods (fig. 58) 
the body is compressed from side to side, and the gills are 
borne on the thoracic region between the legs. These 
forms are familiar to all visitors to the shore under the 




Fig. 57. — Marine Isopod (Idotea 
irrorata). After Harger. 




Fig. 58. — Beach-flea (Gammarus ornatus). From Smith. 

common name of 'beach-fleas/ a name which those 
forms living under dried seaweed, etc., have won for 
themselves through their leaping powers. Others live 



ACER AT A 



231 



in the ocean itself. None of them nave any economic 
importance aside from their acting as scavengers and serv- 
ing as food for fishes. 

Class II.— ACERATA. 

In these arthropods the body is divided into two regions 
a cephalo thorax in front and an abdomen behind. The 
cephalothorax bears the eyes (of which there may be sev- 
eral pairs) and six pairs of appendages, none of which 
can be considered as antennae. The abdomen may have 
or may be without apparent appendages. The respira- 
tory organs are confined to the abdomen, and in their 
development are always connected with the abdominal 
limbs. They may be of three kinds: (1) External gills 
borne on the abdominal legs; (2) internal sacs (lungs) 
with numerous leaf -like folds; (3) air-tubes or tracheae, 
strikingly like those of the Insecta, 
but with a different history. The 
reproductive organs open near 
the middle of the body. 

Subclass I. — Merostomata. 

Here belong the horseshoe 
crabs (fig. 59) of our east 
coast (and a number of fossil 
forms), which breathe by means 
of leaf -like gills; which have 
both simple and compound eyes, 
and which have the bases of 
the walking-feet of the cephalo- 
thorax modified to serve as jaws. 
Recent investigations show that 
the horseshoe crabs are not related to the true crabs, but 
are to be rather closely associated with the scorpions. 




Fig.59. — Horseshoe crab (LimU" 
lus polyphemus). 



232 



SYSTEMATIC ZOOLOGY. 



These forms live in the sea, feeding on worms, etc., found 
in the sea-bottom, coming to the shore in spring and early 
summer to lay their eggs. The horseshoe crabs are without 
any economic importance, as they are useless as food, but 
they are extremely interesting to the naturalist, as they 
are the last remnants of forms which were once abundant 
in the seas of past times. 

Subclass II. — Arachnida. 

With few exceptions, the Arachnids are terrestrial 
forms. They breathe by internal lungs or by tracheae, 
and they lack compound eyes. There are several orders 
of Arachnids, but only a few of them need be mentioned 
here, as some are inconspicuous, while others occur only 
in the warmer regions of the globe. 

Order I. — Scorpionida. 

The scorpions have a single pair of jaws (mandibles) 
and a pair of large pincers, much like those of lobster or 




Fig. 60. — Under surface of scorpion (Buthus) showing the combs and outlines 
of the lung-sacs. 

crab. The long abdomen is distinctly jointed, the seven 
basal joints being much larger than the terminal five. 
The abdomen ends in a very efficient poison-sting. On the 



ACERATA. 233 

lower surface of the basal abdominal segments are the 
openings to four pairs of lungs. Scorpions are not found 
in cold climates, but in the warmer regions they abound, 
and their stings, which rarely prove fatal to man, render 
them unpleasant companions. 

Order II. — Araneida. 
The Araneida, or spiders, have the cephalothorax and 
abdomen unsegmented, but sharply separated from each 
other by a narrow waist. In front are the poison-jaws 
(mandibles), each with a poison-gland inside. At the tip 
of the lower surface of the abdomen are two or three pairs 
of spinnerets. These are modified appendages with num- 
bers of small openings at the tip. Connected with each 
spinneret is a gland which secretes a fluid with the prop- 
erty of hardening as soon as it comes in contact with the 




Fig. 61. — Round-web spider (Epeira insularis). After Emerton. 

air. This is forced out at will through the spinnerets, and 
forms the silk with which the spiders wind their prey, 
wrap up their eggs, and build those marvellous webs, 
interesting to all except the housekeeper. The poison- 



234 



SYSTEMATIC ZOOLOGY. 



jaws are strong, and venomous enough to kill the insects 
upon which these animals feed; but the alleged cases of 
serious or fatal poisoning of man as the result of spider- 
bites need authentication. 

Order III. — Phalangida. 
This name is given to the animals familiarly known 
as 'harvestmen' and ' daddy-longlegs/ with small bodies 
in which there is no waist between thorax and abdomen, 




Fig. 62. — Harvestman {Phalangium pictum). 

and with extremely long legs. These forms feed upon 
small insects, but are perfectly harmless to larger animals. 

Order IV. — Acarina. 
Here belong the mites, in which the unsegmented abdo- 
men is fused to the cephalothorax, and 
in which the first two pairs of appendages 
are modified into a piercing-organ. By 
means of this structure, the ticks burrow 
into the skin of cattle or of man, the itch- 
mite makes its way into the thin skin 
between the fingers, and the red mite 
sucks the juices of plants. As a rule the 
Acarina are parasites, and hence the group 
is largely made up of pests. 




Fig. 63. — Cheese- 
mite, enlarged. 



INSECTS. 



235 



Class III.— INSECTA. 

In the Insects there is a distinct head bearing four 
pairs of appendages — antennae, mandibles, maxillae, and 
labium — which would indicate the existence of at least 
four segments in this region. The respiratory organs are 
tracheae, a system of branching tubes ramifying the whole 
body and opening to the exterior by spiracles in the sides 
of some of the somites. Air is drawn into these tracheae 
by an enlargement of some or all of the 
somites, and forced out again by their con- 
traction. The reproductive organs differ from 
those of other arthropods in having their 
ducts open near the tip of the abdomen. 
The Insecta are divided into Chilopoda 
and Hexapoda. 



Subclass I. — Chilopoda (Centipedes). 

In the Chilopods, which include the 
centipedes and similar forms, the head is 
succeeded by a long series of body-seg- 
ments, each with a pair of locomotor ap- 
pendages (legs), and with no distinction 
between thorax and abdomen. Most of 
the group are carnivorous, and the larger 
forms, at least, are provided with poison- 
glands which open in the first pair of the 
trunk appendages. The chilopods of north- 
ern latitudes are small, insect-feeding forms, 
but in the tropics occur the centipedes, the 
larger species of which are said to be ex- 
tremely venomous. 

Usually the Chilopods are associated with another group, 
the Diplopopa (thousand-footed worms), as a class or 



Fig. 64. — A 
Chilopod 

(Geophilus). 



236 SYSTEMATIC ZOOLOGY. 

subclass, Myriapoda, but the differences between them 
are too great for this. The Diplopods have but three seg- 
ments in the head, and, after the first three, each segment 




Fig. 65. — A Diplopod (Spirostrephon), showing the two legs to a segment* 
From Packard. 

of the body bears two pairs of legs, while the reproductive 
organs open far forward. The thousand-legged worms 
live in moist places, where they feed upon decaying vege- 
table matter. They are harmless forms, but several 
species secrete a strong-smelling substance, which pro- 
tects them against their foes. 

Subclass II. — Hexapoda (Insects). 

The group of Hexapoda contains more species than all 
the rest of the animal kingdom together, a conservative 
estimate placing the number of distinct forms at nearly a 
million. Yet all of these agree in certain essential points. 
Thus, in all, the body is divided into three regions, head, 
thorax, and abdomen, and of these the thorax alone bears 
organs of locomotion. Three pairs of legs are always 
present (whence the name Hexapoda — six-footed — given 
to the group). Of wings, which also are attached to the 
thorax, there may be one or two pairs. The head bears 
four pairs of appendages, one pair (the antennae) being 
sensory; the others (mouth-parts) being used in eating. 
The sexes are always separate, and the reproductive organs 
open at the hinder end of the body just beneath the vent. 

In the head no evidence of segments is seen, except as. 



INSECTS. 237 

shown by the appendages. The antennae, of which there 
are only a single pair, are sensory in function. In many 
cases they clearly bear organs of smell, and in some they 
may also be hearing-organs. In the primitive condition 
the mouth-parts are fitted for biting and eating hard sub- 
stances, the mandibles being strong jaws, while the max- 
illae and labium serve to hold the food in place. These 
latter bear jointed prolongations — the palpi — which are 
sensory. In other insects these mouth-parts are modified 
and united into a sucking-tube which frequently is a 
piercing-organ of no mean capabilities. This sucking-tube 
is variously constituted in the different orders of hexa- 
pods. Usually the labium forms the chief part of the 
organ, the other parts (mandibles and maxillae) playing 
inside the labial tube, but in the butterflies the tube is 
formed from the maxillae, the other parts being greatly 
reduced . 

The thorax is composed of three segments, named, from 
in front backwards, the prothorax, mesothorax, and meta- 
thorax. Of these the first is frequently movable upon the 
next. Each segment bears a pair of legs, made up of 
several joints, the number varying according to the num- 
ber in the foot (tarsus), the rest of the member usually 
consisting of four joints. On the dorsal surface of the 
meso- and metathorax occur the wings, the characters of 
which are largely used in the classification of insects. 
They are entirely lacking in the lowest insects (Thysanu- 
ra) as well as in individuals of other groups, as worker 
ants, many parasites, and the females of certain moths. 
In the flies the posterior wings are greatly reduced, so 
that they appear like a pair of knobbed hairs, termed 
' balancers/ since if they be removed the fly cannot con- 
trol its motions. Frequently both pairs of wings are 



238 



SYSTEMATIC ZOOLOGY. 



used in flight, but in certain groups the front pair are 
much thickened and hardened, so that they are converted 
into wing-covers {elytra) which protect the hinder wings 
when at rest. 

The abdomen is normally composed of ten segments, 
but this number may be reduced. In some insects the 
abdomen joins the thorax by its whole width, while in 
others it is contracted in front to a slender stalk as in 
the ants and wasps. The appendages of the abdomen 
are never locomotor in function in the adult. In the 
lowest insects rudimentary appendages may occur on all 
segments of the abdomen, but in the higher groups only 
three pairs, at most, occur, and two of these are modified 
into an organ (ovipositor) for laying the eggs. In the 
bees, wasps, etc., the ovipositor is at the same time an 
offensive weapon, the sting, there being connected with it 
a poison-gland in the abdomen. 

The alimentary canal has few convolutions. Into the 
mouth-cavity open the salivary glands.* In those forms 
which eat solid food like the crickets and grasshoppers a 
1 chewing-stomach ' with hard horny teeth occurs. Behind 




Fig. 66. — Diagram of hexapod anatomy, b, brain ; c, crop ; h, heart ; m, Mal- 
pighian tubes; r, reproductive organs; s, stomach; sg, salivary glands; v, 
ganglia of ventral chain. 

this comes the true stomach, and following this the intes- 
tine, to which are attached a varying number of Malpighian 
* The 'molasses' of the grasshopper is the saliva. 



INSECTS. 239 

tubes (2-100 or more) which, like the kidneys of higher 
forms, serve to carry away nitrogenous waste from the 
body. 

The circulatory organs are poorly developed. A dorsal 
tube, the heart, is present, lying above the alimentary 
canal, and this pumps the blood forward, into an aorta of 
varying length. Soon, however, the blood leaves this 
tube and flows between the muscles and viscera and finds 
its way to the hinder part of the body, where it again 
enters the heart through openings in its sides. This im- 
perfection in the blood-vessels is compensated for by the 
peculiar character of the organs of breathing (respiration). 
These consist of a number of tubes (tracheal) which open 
to the outside by paired openings (spiracles) in the sides 
of the body. These spiracles occur in the thorax and 
abdomen, and never exceed a pair to a somite, and from 
three to ten pairs may occur. Internally the tracheae 
branch again and again, until the finest twigs penetrate 
to every part of the body. Frequently the various tracheae 
are connected on either side of the body, and in the strong- 
fliers these connecting tubes are enlarged into air-sacs, 
which thus render the body lighter. Air is drawn into 
the tracheae by the enlargement of the abdomen, and 
thus reaches all of the tissues of the body. Since breath- 
ing is accomplished through the spiracles in the sides of 
the body, one can see that one cannot readily kill an 
insect by putting chloroform on its head. 

The nervous system consists of an enlargement or 
'brain' in the head, in front of the mouth, and from 
this nerves go to the eyes and antennae, while a stronger 
nerve-cord passes on either side of the gullet, to unite 
in a second enlargement (ganglion) behind. Thus, as 
will readily be understood, the alimentary canal passes 



240 SYSTEMATIC ZOOLOGY. 

through the nervous system, a condition which is totally 
different from anything found in the vertebrates. Be- 
hind this second or infracesophageal ganglion a double 
nerve-cord extends along the floor of the body, connect- 
ing a series of similar ganglia. In the lower insects there 
is a ganglion in each segment, but in the higher these tend 
to move forward and to unite with each other into a few 
masses or compound ganglia. It will thus be seen that 
this nervous system is strikingly like that of an annelid 
or crustacean. 

The eyes are always on the head. In the adult insects 
compound eyes are usually present, and besides these 
there may also be simple eyes or ocelli. In the latter 
there is but a single lens, while the compound eyes are 
composed of many distinct visual structures, each with its 
own lens. Organs, which are regarded as ears, occur in 
various forms. In the grasshoppers these organs are on 
the base of the abdomen; in the crickets, on the legs; in 
many groups the antennae are supposed to have auditory 
powers. Taste resides chiefly in the lower lip, while 
touch, though found all over the body, is especially devel- 
oped in the antennae and the palpi of labium and maxillae. 
In some insects the sense of smell is strongly developed, 
and there is reason to believe that the olfactory organs 
are in the antennae. 

The group of Insecta may be subdivided in two ways, 
accordingly as different characters are employed. If we 
follow one method the mouth-parts form the basis of 
division, and we have a mandibulate group in which the 
jaws are fitted for biting, as in the grasshopper and beetle; 
while in the haa stellate group the mouth-parts are no 
longer fitted for biting, but form a tube through which 
liquid food is sucked, as in the bugs and butterflies. 



INSECTS. 



241 



The second method of subdivision depends upon the 
facts of life-history. In the first or ametabolous group the 
young leaves the eggs with the general shape and appear- 
ance of the adult, the chief difference being that of size. 
In the second or hemimetabolous division the young upon 
leaving the egg differs from the adult in the lack of wings. 
During growth the skin is often molted, and with each 




Fig. 67. — Life-history of the Colorado potato-beetle (Doryphora decemlineata*) . 
a, eggs; b, larva; c, pupa; d, adult. 



molt the wings increase in size until at last the adult 
condition is reached. In the third or holometabolous group, 
a form, the larva, hatches from the egg, which differs 
greatly from the adult. This increases greatly in size 
but without marked change in appearance, until, at a 
single molt, it changes its appearance completely and 
becomes a pupa, in which condition it remains quiescent 
until by a final molt the adult characters are assumed 
(fig. 67). These changes constitute a metamorphosis. 



242 SYSTEMATIC ZOOLOGY. 

These two classifications do not agree, as can be seen 
from the following tables: 

Mandibulatle. Haustellat^e. 

Thysanura. Hymenoptera.* 

Orthoptera. Hemiptera. 

Pseudoneuroptera. Lepidoptera. 

Neuroptera. Diptera. 
Coleoptera. 

Ametabola. Hemimetabola. Holometabola. 
Thysanura. Orthoptera. Coleoptera. 

Pseudoneuroptera. Neuroptera. 
Hemiptera. Hymenoptera. 

Lepidoptera. 
Diptera. 

A word may be added concerning this metamorphosis. 
The holometabolous condition has doubtless been intro- 
duced in order to allow the larva to retain its shape as 
long as possible, and the changes, which are gradual in 
the hemimetabolous group, are here condensed into the 
last two molts. Hence the pupal condition is one of 
great change, and consequently it would be inconvenient, 
if not impossible, for the animal to feed at this time. 
So the stage here becomes one of rest, so far as externals 
are concerned. 

As will be seen from the foregoing tables, the group of 
Hexapoda, or Insecta, is subdivided into nine groups or 
orders, f 

* The Hymenoptera have the mouth-parts adapted for both 
biting and sucking. 

f Many authorities recognize more orders than these, the differ- 
ence chiefly lying in the extent to which the Neuroptera and Pseu- 
doneuroptera are subdivided. 



INSECTS. 



243 



Order I. — Thysanura. 

These are small wingless insects without any general 
common name except those of ' bristle- 
tails' and ' springtails,' which have been 
manufactured for them. The springtails 
live in damp places — in cellars, under 
leaves in the forest, etc., and they have 
a spring beneath the body by means of 
which they can jump to great distances. 
The bristletails have the body terminating 
in two long filaments. To this last group 
belong some pests known commonly as 
' silverfish ' — soft-bodied shining forms, 
which eat paper, starched clothing, etc. 
Aside from this silverfish or 'fish-moth' 
the group has little general interest; but 
to the naturalist it is very interesting 
because it is so primitive. 




Fig. 68. — 'Silver- 
fish' {Lepisma 
saccharina). 



Order II. — Orthoptera. 

The name Orthoptera, which is given to the group 
containing the grasshoppers, crickets, locusts, cockroaches, 
etc., means straight-winged, and alludes to the general 
course of the veins of the wings of most forms. This is, 
however, not a feature of great importance, for indeed we 
find species which are absolutely lacking in wings, but 
which are, in other respects, so closely related to the 
grasshoppers that they too must be included in the Orthop- 
tera. When we take all of these Orthopterous forms we 
see that they agree in a number of points, some of which 
may be mentioned. The jaws are strong and fitted for 
biting hard substances; the antennae are usually long and 



244 SYSTEMATIC ZOOLOGY. 

thread-like; ocelli are always present; the prothorax moves 
freely on the mesothorax; the abdomen is ten-jointed, and 
it usually bears on its tenth somite movable cerci; the 
ovipositor is large and cannot be withdrawn into the 
abdomen; the anterior wings serve as covers for the second 
pair, and these last are folded longitudinally, when at rest, 
like a fan. 

Besides these points, which should have been made out 
by the student, there is another feature not readily dis- 
covered in the classroom. The young Orthopteran hatches 
from the egg with all the legs and segments of the adult, 
which it resembles much in general appearance, except in 
the following particulars: it is smaller in size, with a dis- 
proportionately large head, and it lacks the wings character- 
istic of the full-grown form. It is most voracious, and 
with much eating increases rapidly in size. But since it is 
enclosed in a hard outer wall, incapable of growth, it has 
frequently to cast off this non-elastic 'skin' and to grow 
a new one, larger than the old. This molting is accom- 
plished by a splitting of the old skin down the back, and 
from this hole the animal draws itself, and now, its skin 



Fig. 69. — Young grasshopper with the wings just beginning to appear 
After Emerton. 

being soft, it can readily increase in size. Gradually, 
however, the skin becomes thicker and harder, and the 



INSECTS. 



245 



process of molting must be repeated. With each of these 
molts the animal grows more like the adult, the wings 
appearing first as small pads upon the back (fig. 69) , and 
with later molts attaining the final size. In other words, 
the Orthoptera are hemimetabolous. It is an easy, matter 
to follow these changes by catching the young hoppers in 
the spring, and keeping them in a breeding-cage, feeding 
them frequently with fresh grass and leaves. The student 
must keep this history in mind 
when studying the peculiarities 
of the beetles. 

With few exceptions the Or- 
thoptera are injurious to human 
interests, since they are vegetable- 
feeders, and, as they often occur 
in immense numbers, they can 
destroy all crops throughout large 
districts. 

Possibly the most disagreeable 
members of the group are the 
cockroaches, flattened forms, 
many of them wingless, which are 
familiar from the persistence with 
which they haunt our dwellings, 
etc., after they have once been 
introduced. Our familiar ' Croton 
bug' is an immigrant from 
Europe, but we have also our 
native species. Insect-powder 
and eternal vigilance are the 
only means known to rid a build- 
ing of these pests. 

Strangest of our Orthoptera are the 'walking-sticks'; 




Fig 



70. — Tropical walking- 
stick (Acanthoderus). From 
Hertwig. 



246 SYSTEMATIC ZOOLOGY. 

long, wingless animals which feed upon the oak and which, 
as they stand motionless upon a twig can scarcely be dis- 
tinguished from the twigs themselves. The species figured 
is foreign. 

Grasshoppers and locusts are much alike, and are usu- 
ally confused by most people. Both are leaping forms, 
but the locusts have short antennae and short ovipos- 
itors, while the grasshoppers have these parts long. The 
katydid is a grasshopper, while the 'grasshopper' which 
in 1873-76 did much damage in our western states is a 
locust. Closely allied are the crickets, whose ceaseless 
chirp is so monotonous upon summer nights. These make 
their song by rubbing their wing-covers together, and it is 
interesting that only the male can make the noise.* The 
1 ear ' of the cricket is not upon the abdomen but upon the 
fore legs. It is not certain that any of these structures 
are really for hearing. 

Order III. — Pseudonetjroptera. 

These forms, like the Orthoptera, have biting mouth- 
parts, and have a gradual change from the young to the 
adult, but they differ from those forms in having both 
pairs of wings alike, usually very thin, and transparent, 
with very numerous veins, and not capable of being folded 
like those of the Orthoptera. There are two divisions of 
these Pseudoneuroptera. In the first the younger stages 
are passed in the water, in the second on land. 

Examples of the first are seen in the dragon-flies 

* It has been pointed out that the number of chirps of the crickets 

is dependent upon temperature, and that in the northern states 

n — 40 
the temperature can be ascertained by the formula !T = 50-| -r — , 

in which T stands for temperature and n for the number of chirps 
per minute. 



INSECTS. 



247 



(Odonata); their larvae live in the water, where they 
feed upon other insects, etc., and especially on the larvse 
of mosquitoes. When the adult stage is reached and they 
take to the air, they are veritable dragons, feeding upon 
insects, which they catch on the wing. Here, too, belong 
the May-flies or day-flies with an aquatic life of from one 
to three years, a life in the air of but a few days, or even a 
few hours. These May-flies often appear in great numbers 
in the cities near the Great Lakes. 

The celebrated white ants or termites (fig. 71) may 
represent the forms with a solely terrestrial life-history. 
These are not ants at all in the true sense of the word, but 




Fig. 71. — White ant (Termes flavipes). a, larva; &, winged male; c, worker; 
d, soldier; e, queen; /, pupa. From Riley. 

they resemble them in several points. They form large 
colonies consisting of several distinct ' castes ■ with different 
structure. Only the kings and queens are winged, and only 
these are capable of reproduction. Besides these there 
are 'workers' and ' soldiers.' The workers build the 
nests, gather the food for the whole colony, and bring 



24S SYSTEMATIC ZOOLOGY. 

up the young. The soldiers have enormous heads, and 
protect the others. The termites are miners, and make 
their burrows beneath the earth and inside of dead wood. 
They avoid the light, and where they cannot otherwise 
make their way they build covered ways, sometimes for 
hundreds of feet. They feed upon dead wood, and will 
sometimes utterly eat out the inside of the timbers of a 
house, leaving posts and joists but a mere shell. They 
are comparatively rare in colder climates, although they 
occur as far north as New Hampshire, but in the tropics 
they become a terrible pest. The queen (fig. 71, e) is kept 
a prisoner in the nest, is fed by the workers, and develops 
so many eggs that her abdomen is swollen out of all pro- 
portion to the head and thorax. As the eggs escape they 
are cared for by the workers. 

Order IV. — Netjroptera. 

These forms have the wings much as in the Pseudoneu- 
roptera, the mouth-parts for biting are much reduced, but 
they have a complete metamorphosis. The majority of 
these forms are inconspicuous, and their existence is hardly 
recognized except by naturalists. Here belong the 'dob- 
sons/ or hellgrammites, larvae of a large insect, which are 
used as bait by anglers. Here, too, belong the ant-lions, 
which build little pitfalls for the ants on which they feed. 
Last to be mentioned are the caddis-flies or case-flies, the 
aquatic larvae of which protect themselves by building 
cases of stones, sticks, etc., in which they hide and which 
they carry about with them in their search for food. 
These caddis-flies, in the adult stage, have the mouth- 
parts much reduced, and are supposed to represent pretty 
closely the ancestors of the butterflies and moths (Lepi- 
doptera) . 



INSECTS. 



249 




Fig. 72. — Adult male hellgrammite (Corydalis comutus). From Riley 




Fig. 73. — Adult ant-lion {Myrmeleon). 



250 SYSTEMATIC ZOOLOGY. 

ORDER V. — COLEOPTERA. 

The beetles are all grouped under the common head of 
Coleoptera, the name of which means sheath- wings. Of 
beetles there are known over a hundred thousand different 
kinds, but all these agree in the following points: The 
mouth-parts are fitted for biting; ocelli rarely occur; the 
prothorax is large; the anterior wings are converted into 
thick, horny wing-covers or elytra, beneath which are 
folded the much larger hinder wings. 

From the egg of the beetle there hatches out a some- 
what worm-like form popularly known as a 'grub.' This 
larva (fig. 67, b), as it is called, bears but the slightest re- 
semblance to its parents. It eats and grows, without 
essentially altering its appearance until at last it under- 
goes a molt which results in a sudden change in its appear- 
ance. It is no longer worm-like, but looks more like the 
adult beetle. This stage, the pupa (fig. 67, c), does not 
eat, but lies quiet in some cavity; after a longer or shorter 
period of rest it molts again and emerges the perfect 
beetle, after which, no matter how long it may live, it under- 
goes no further changes nor does it increase in size. In 
other words the beetles are holometab- 
olous and, together with the Lepidop- 
tera, afford the best-known examples of 
a complete metamorphosis. 

The beetles are divided into two great 
groups. In the one (Rhynchophora) that 
part of the head which bears the mouth 
is prolonged into a snout; in the other 
there is no such prolongation. These 
nut-weevil (Ba- are ca n e d the normal Coleoptera. 

lamnus nasicus). * 

The snout beetles (Rhynchophora) or 
true weevils are all injurious, since as larvse and adults 




INSECTS. 251 

they feed upon vegetation. Some attack fruits, some 
eat grain, and others nuts. Certain ones burrow between 
the bark and solid woods of trees, excavating curious mines, 
while others bore into the solid wood. 

Of the normal Coleoptera some are beneficial to man, 
since they feed upon other insects. Here may be enumer- 
ated the brilliant tiger-beetles and the caterpillar-hunters, 
the habits of which have given them their common names. 
They are all extremely active. The water-beetles should 
be placed in the same category, for they and their larvae 
feed upon the insects of our streams and ponds, and do 
not a little towards keeping the mosquitoes within bounds. 

Another large group of beetles have the antennae ending 
in a club or knot. Some of these, like the carrion-beetles, 
are of value, since they lay their eggs in decaying flesh, 
where the larvae live and nourish, converting what other- 
wise would be a nuisance into another crop of beetles. 
Others, like the 'ladybugs,' are predaceous, feeding upon 
the smaller insects; but still others are unmitigated nui- 
sances, since they have a taste for dried animal matter. 
Among these are the bacon-beetle and the far better known 
1 buffalo-bug/ which plays havoc with our silks and wool- 
ens, our carpets, and the specimens in our museums. In 
this same group belong the rove-beetles, forms in which the 
wing-covers are very short, not covering half of the long 
abdomen. Disturb one and notice the threatening way it 
moves its abdomen about, as if to sting. It is, however, 
perfectly harmless. 

The spring-beetles and the fireflies agree in having the 
antennae toothed something like a saw. The spring-beetles 
receive their common name from the fact that when laid 
upon their backs they will suddenly throw the body into 
the air. When opportunity offers, study the actions of one 



252 SYSTEMATIC ZOOLOGY. 

of these and see how the spring is arranged. Some of 
these spring-beetles are serious pests, for their larvae are the 
well-known wire worms. The fireflies are interesting from 
their phosphorescent powers. Underneath the abdomen 
are the light-giving spots. Much attention has been given 
to this light-producing apparatus in the hope of obtaining 
a solution of the problem of producing light without heat. 

A large number of beetles have the terminal portion of 
the antennae, like that of the June-bug, with a club formed 
of leaf-like joints. These are known as Scarabaeans, from 
the sacred beetle (Scarabceus) of the Egyptians which 
belongs to the group. These sacred forms are repre- 
sented in our country by the tumble-bugs, which lay their 
eggs in balls of manure which they trundle along the road 
until they find a suitable place to bury them. From the 
similar habits of the Scarabaeus the Egyptians worked out 
quite a symbolism. "The ball which the beetles were 
supposed to roll from sunrise to sunset represented the 
earth; the beetle itself personified the sun, because of the 
sharp projections on its head, which extend out like rays of 
light; while the thirty segments of its six tarsi represented 
the days of the month." Other members of the Scara- 
baeans, like our June-bugs, are vegetarians and do no little 
damage. As larvae they feed upon the roots of grass 
and other plants; as adults they devour foliage. In 
the tropics occur Scarabaeans of enormous size, some hav- 
ing bodies six inches in length. 

The long-horn beetles live as larvae in the solid portions 
of trees and shrubs, where they bore long tubes. The 
species usually have long antennae, and many of them are 
beautifully colored. Structurally much like these borers 
are the shorter and more oval leaf -beetles, which do so much 
damage. Here belong the cucumber-beetles, the Colorado 



INSECTS. 



253 



potato-beetle (fig. 67), and others which feed upon the 
grape, the asparagus, etc.; and near them are the so-called 
weevils (fig. 75) which attack peas and beans. 

The oil-bottles and blister-beetles are a curious group, 
since in their young stages 
many of them are parasitic 
upon other insects, while 
when adults they contain a 
peculiar substance which 
will raise a blister upon 
human flesh. Hence some 
of these are killed, dried, 
and form a regular article of 
commerce under the name 
of Spanish flies and are used in the manufacture of blis- 
tering-plasters. 




Fig. 75. — Pea-weevil (Bruchus pisi), 
natural size and enlarged. b, pea 
containing a weevil. 



Order VI. — Hymenoptera (Bees, Wasps, Ants). 

Bees, wasps, and ants are the better known represen- 
tatives of this group, all the members of which agree in 
having four membranous wings (the front pair the larger) 
with comparatively few cross-veins. The mouth-parts are 
fitted both for biting and for sucking. There is a com- 
plete metamorphosis. So far as we can judge, these are the 
most intelligent of all insects, and the student who investi- 
gates their habits is continually rewarded by new facts, 
which show that their small brains are most highly devel- 
oped. In other points of structure, however, they are 
much less complicated. 

In the lower forms the female is provided with an ovi- 
positor, frequently of great length, which is well adapted 
for boring. In the higher this ovipositor is modified into 



254 



SYSTEMATIC ZOOLOGY. 



a sting — a weapon of offence and defence, the efficiency of 
which is increased by an associated poison-gland. 

The lowest forms are the sawflies, the larvae of which are 
vegetable-feeders, some eating the leaves of plants, others 
boring in the solid wood. A little higher in the scale come 
the gall-flies, those forms which lay their eggs in various 




Fig. 76. — Ichneumon-fly, enlarged. From Riley. 

plants and in some way so stimulate the vegetable tissue 
that strange growths — galls — are formed. Allied to these 
last are the ichneumon-flies (fig. 76), which lay their eggs 
in other insects. Here the larvae hatch out, feed upon the 
host, at last destroying it. Then pupation comes, and 



INSECTS. 255 

the perfect insect emerges to repeat the process. Natu- 
rally these ichneumon-flies are an important agent in keep- 
ing down injurious insects. 

The ants are possibly the most interesting of all insects. 
They are true communists. In them, as in the white 
ants (p. 247), there is a differentiation of the individuals 
into males, females, and workers, the latter being wingless. 
Any adequate treatment of these forms would of itself 
demand a book larger than this volume. The males and 
females take 'wedding -flights,' after which the male soon 
dies, while the females bite off their wings and henceforth 
have nothing to do except to lay eggs. These eggs are 
cared for by the workers, which, as the name implies, 
perform all the labor of the colony. They obtain the 
food, take care of the immature insects, build the nests, 
and carry on the wars. In their battles some ants always 
take prisoners, and these are kept as slaves. Some species 
of ants have depended on slaves so long that they are only 
able to fight, while did the slaves not feed them they would 
starve. No group of insects will better reward careful 
study than these. 

The digger-wasps make mines in the earth or in wood in 
which they lay their eggs, usually placing with the eggs a 
supply of food for the young. Some use as food pollen 
and nectar of plants, while others store up insects or spiders 
which have been so stung that they are paralyzed, not 
killed. In this way the food will keep for a long time. 

Some true wasps are solitary, some colonial, and in 
the colonial forms we find again, as in the ants, males, 
females, and workers, the workers being winged. Most of 
these true wasps (and hornets are wasps) build nests usu- 
ally of half -decayed wood, which they chew into a kind of 
paper. Thus the wasps were the earliest makers of wood- 



258 SYSTEMATIC ZOOLOGY. 

pulp paper. Inside are the , cells in which the eggs are 
placed and in which the young undergo their metamor- 
phosis. Males and workers die in the autumn, but the 
females live through the winter and start new colonies in 
the spring. 

Among the bees the honey-bees occupy the first place 
from their value as honey-storers. Indeed, so great is 




Fig. 77. — Sand-wasp (Sphex). 

their value that hundreds of books and dozens of journals 
have been published dealing wholly with them. In each 
colony there are males (drones), females (queens), and 
workers, the latter imperfectly developed females. Soon 
all the drones are killed, and all the queens except one, 
and her sole duty is to lay eggs. If the queen be lost, the 
workers can take a larva that would otherwise develop 
into a worker, and by different food convert it into a 
queen. Wax is a secretion of the bee, honey is the nectar 
obtained by the bees from flowers, while the bee-bread is 
the pollen of flowers. 



INSECTS. 



257 



Order VII. — Hemiptera (Bugs). 

The Hemiptera are the true bugs. The term bug is fre- 
quently loosely applied, but any true bug has the follow- 
ing characteristics: Its mouth-parts are not fitted for 
biting, but for piercing and sucking. They are prolonged 




Fig. 78. — Head of seventeen-year locust to show the mouth-parts, etc. a, an- 
tennae ; e, compound eye ; I, labium ; md, mandible ; mx, maxilla. 

into a beak, consisting of a fleshy grooved sheath (labium) 
with four needle-like bristles (mandibles, maxillae) in the 
groove. This organ is used for making holes in plants or 
flesh, and also serves as a tube through which the bug sucks 
up the juices found. The bugs have an incomplete meta- 
morphosis, are hemimetabolous (p. 241), hatching from the 
egg much in the adult condition, except that wings are 
lacking. 



258 SYSTEMATIC ZOOLOGY. 

Almost all the Hemiptera, when adult, have four wings, 
though there are a number of wingless forms. These 
wings are built upon two distinct patterns, and this serves 
as a means of subdividing the Hemiptera into two groups. 
In the one (Heteroptera) the basal half of the anterior 
pair of wings is thickened while the rest is membranous, 
and the wings themselves are held in an overlapping man- 
ner upon the back when at rest. This condition is familiar 
in the squash-bug. In the other group (Homoptera) 
there is no such thickening of the basal portion of the first 
pair of wings, and these organs, when at rest, are placed 
upon the sides of the abdomen. 

While most of the bugs are injurious to human interests, 
there are some which are a benefit to man, since they feed 
on injurious insects; and still others, like the cochineal - 
and lac-bugs, produce substances of value to man. 

Of the Heteroptera some are aquatic, and of these 
the water-skaters, gliding over the surface of still water, 
are familiar to all. Others live most of their lives beneath 
the surface, and some of the larger of these water bugs, 
especially those called ' electric-light bugs/ can kill small 
fish, sticking the beak into them and sucking their blood. 

Of the terrestrial forms none is more widely known than 
the bedbug, a form which is famed for its attacks on man. 
It is one of the bugs which never develop wings. From 
the pecuniary standpoint the cinch-bug is more important, 
since it attacks fields of grain, doing sometimes millions of 
dollars of damage in a single year. The young attack first 
the roots and underground stems, and later the stems them- 
selves, killing them before they have had time to ripen the 
grain. 

The squash-bug, which does such damage to pumpkin- 
and squash-vines, is another form of Heteropteran, as are 



INSECTS. 



259 



those familiar forms which have no other common name 
than ' stink-bug.' No one who has ever taken into his 
month a berry over which one of these animals has trav- 
elled can doubt the appropriateness of the name. How- 
ever, these bugs are not alone in their malodorous qualities; 
many others, like the squash-bug and bedbug, also secrete 
a strong-smelling fluid, which of course protects them 
from birds and other insect-eating animals. 

Among the Homoptera the cicadas come first. One of 
these, the 'dog-day locust' (it is not a locust at all), is 
familiar from its shrill note heard during the hottest 
days of summer. This form requires two years to come 




Fig. 79. — Seventeen-year locust (Cicada septendecim). From Riley, a, pupa; 
b, pupa-case from which the adult, c, has escaped; d, twig bored for the 
deposition of eggs. 

to its full maturity, but its cousin, the seventeen-year 
locust (fig. 79), requires, typically, seventeen years from 



260 SYSTEMATIC ZOOLOGY. 

the time the eggs are laid until the animals are ready to 
lay another series of eggs. These eggs are laid in the 
twigs of trees. The young when hatched from these eggs 
drop to the ground, and, burrowing beneath its surface, 
spend the next seventeen years * sucking the juices of 
the roots of the trees. 

Another group of Homopterans are the 'spittle-in- 
sects,' small forms which, settling upon a blade of grass 
or twig of shrub, soon surround themselves with a frothy 
mass. They suck the juices of the plant, and after having 
taken out what they desire eject the rest as a mass of foam. 
Examine one of these bits of froth and you will find the 
immature bug inside. Allied to them are the tree-hoppers 
and leaf-hoppers, so common and so injurious to vegeta- 
tion. 

The plant-lice, or aphides, deserve a little more atten- 
tion. They occur on almost every kind of plant, sucking 
its juices and reproducing as rapidly as possible. One 
does but little damage, but the havoc wrought by thou- 
sands is very considerable. In the summer the colonies 
of these forms will be found to be largely wingless, and 
these wingless forms are all females, capable of reproduc- 
tion without males. In some species they lay eggs, in 
others they bring forth living young. These in time 
reproduce in the same way, and so rapidly do they in- 
crease that one plant-louse may be the progenitor of 
100,000,000 'in five generations. At the close of the season 
the true sexual forms appear, the males always winged. 
These sexual forms produce eggs which last through the 
winter. All of the plant-lice are destructive to vegeta- 
tion, and some, like the Phylloxera of the grape, are ex- 
tremely so. 

* In the South the period is thirteen years, in the North seventeen. 



INSECTS. 261 

The scale-bugs and bark-lice (Coccidse) are also serious 
pests, doing great damage to fruit-trees, etc. The males 
are winged, but the female is scale-like and adheres closely 
to the branch or the fruit, sucking its juices. Oranges and 
lemons are frequently covered with these forms. A few, 
however, are of value to man. The pigment carmine is 
made from the dried bodies (cochineal) of a scale-louse of 
the cactus, while lac — from which shellac is prepared — is 
the secretion of a tropical tree-inhabiting species. 

Besides the Heteroptera and the Homoptera, the Hemip- 
tera embraces a third division, the Parasita, or lice. 
These are all wingless forms, living as parasites in the 
hair and on the skin of mammals, and sucking the blood 
of their hosts. 



Order VIII. — Lepidoptera (Moths and Butterflies). 

The millers, moths, and butterflies are grouped together 
as Lepidoptera, and all agree in having four membranous 
wings covered with dust-like scales, in having a long suck- 
ing ' tongue' formed of the two maxillae, and in having 
a complete metamorphosis (p. 241) in which there hatches 
from the egg a worm-like larva (fig. 80). This stage is 
commonly known as a caterpillar or 'worm/ but it differs 
from all true worms in having legs, and those who wish to 
call things by their true names should never speak of 
them as worms. These larvae always have sharp jaws and 
simple eyes, and are provided with from eight to sixteen 
legs. Of these, three pairs are on the thoracic segments, 
while the abdomen has from one to five pairs. These 
larvae, when they hatch from the egg, are small, but by 
feeding they grow, increase in size being rendered possible 
by frequent moltings of the skin. At last there comes a 



262 



SYSTEMATIC ZOOLOGY. 



molt by which the appearance is greatly changed and 
the pupal stage is reached. In the pupa (fig. 81) the 
abdominal legs are lost, the body is shortened and covered 
with a harder skin, in which one can trace the legs, an- 
tennae, and wings of the future moth or butterfly, folded 
over the breast. Many caterpillars of the moths, as a 
preparation for pupation, spin silken nests or cocoons, 
the silk being the product of glands which empty into the 
mouth. The pupae of butterflies have usually no such 
silken protection, but are free. From the fact that many 





Fig. 80. — Army-worm, larva of Leu- 
cania unipuncta, showing five (pairs 
of) abdominal legs. 



Fig. 81. — Pupa of a Bombycid moth- 
a, antenna ; I, first pair of legs ; w, 
wings. 



of these butterfly pupse are marked with patches and 
spots of gold, they are frequently called chrysalides (sing. 
chrysalis) . 

The pupal stage lasts for some time (months), during 
which no food is taken and no motion possible except of 
the abdominal rings; then the pupal skin is molted and 
the perfect insect (imago) (fig. 82) emerges. In those spe- 



INSECTS. 263 

cies which have a cocoon the silken threads are softened 
by fluids secreted by the imago, and in some there are 
hooks at the bases of the wings which aid in tearing an 
opening for the escape of the moth. 

When the imago first comes out it is soft and flabby, 
and the wings are soft bags. They are rapidly distended 




Fig. 82. — Army-worm moth (Leucania unipuncta). From Riley. 

by blood pumped into them, and, held expanded, are 
rapidly dried by the air into efficient organs of flight. 
The wings are covered with scales, and to these the color- 
pattern is due. These scales are merely modified hairs 
like those which cover the whole body. When removed 
the wing is seen to have a framework of supporting nervures 
or 'veins' which are really not veins at all. These veins 
vary greatly in their arrangement in different moths and 
butterflies, and are used as a basis of classification. 

While the larvae are biting insects, the adult is adapted 
for taking liquid nourishment by means of a so-called 
1 tongue' which when not in use is coiled beneath the head 
like a watch-spring. This tubular structure, which, in 
function, is so like the beak of the bugs, is much different 
in structure, as it is formed by the union of the two max- 
illa, while the other parts — labrum, mandibles, maxillary 



264 SYSTEMATIC ZOOLOGY. 

palpi, and labium, are present, but in a more or less re- 
duced condition. 

There are two great divisions of the Lepidoptera, the 
butterflies and the moths of common language. The day- 
flying butterflies hold the wings erect over the back when 
at rest, and they have the antennae enlarged into clubs 
at the tip. In the moths, which are mostly nocturnal, 
the wings are carried nearly horizontally when at rest, 
and the antennae, while frequently feathered, are never 
clubbed. 

Among the smallest, and at the same time the most 
troublesome, of the moths are those pests, the clothes- 
moths and their relatives, which do such damage to 
woolen goods, furs, etc. These are among the few larvae 
of moths which have left a vegetarian diet and taken to 
food of animal origin. Another exception is found in 
the bee-moth, the larva of which is found in apiaries, 
feeding upon the wax and spinning its silk all through 
the comb. 

Of the leaf-rolling moths the codling-moth is the best 
known. Its larva is the worm so frequently found near 
the core of apples. Other allied species tie the leaves of 
apple-trees, rose-bushes, etc., together and live in the nest 
thus formed. 

The Geometrids include those moths whose larvse are 
commonly known as measuring-worms from their looping 
gait. All of these are pests, and the canker-worms exceed 
all the rest in this respect. These are especially noticeable 
from the fact that the adult female is wingless. 

The sphinx-moths or hawk-moths are large narrow- 
winged forms, the larvae of which are injurious to many 
plants. From the attitude assumed by some larvae when 
at rest the name sphinx was applied to the group; the 



INSECTS. 265 

other common name, hawk -moths, has reference to their 
powers of flight. 

Another group of moths are known as Bombycids. 
While some of these are unmitigated pests, others are of 
value to man, the silkworms leading in this respect. These 
are, in fact, the most valuable of all insects. The true 
silkworm is a native of China, but has been distributed to 
all of the warm parts of the earth. Like other caterpil- 




Fig. 83. — Sphinx-moth (Everyx myron). From Riley. 

lars, they form their cocoons, and then these are heated 
to kill the pupa and the silk of the cocoon is unwound, 
and after proper treatment becomes the silk of commerce. 
We have several species of silkworms in this country 
some of which make a stronger silk than the Chinese 
species; but although a few articles have been made 
from it, it has no economic importance. These large 
American silkworm-moths are known as Polyphemus-, 
Prometheus-, Cecropia-, and Io-moths, and they, together 
with the beautiful green Luna-moth, are great favorites 
with collectors. 

The skippers are a group of small butterflies in which 
the clubbed antennae are bent into a hook at the tip. They 
are called skippers on account of their jerky flight. 



266 SYSTEMATIC ZOOLOGY. 

The swallowtails are well-known forms of butterflies in 
which the hind wings are prolonged into tails, whence the 
name. The larvae of these forms are usually brightly col- 
ored, but they are protected by a pair of 'stink-horns/ 
which they can project at will from the region of the neck, 
and which give off, in most cases, a most offensive odor. 

Another group of butterflies, whitish yellow or orange 
in color, are typified by the cabbage-butterflies. We had 
some of these which were bad enough ; but a few years ago 
the European cabbage-butterfly came to this country and 
became the greatest pest of all our butterflies. 

Of smaller size — the most delicate of all our butterflies 
— are those forms which have received the common names 
of the blues, the coppers, and the hair-streaks, from their 
predominant colors and from the ornamentation of the 
wings. 

Of larger size are the group of ' four-legged' butterflies 
(fig. 84), so called because the first pair of legs are so small 




Fig. 84. — A four-legged butterfly (Argynnis aphrodite), under side shown 
on right. 

as to be of no use to the animal. Of these forms there are 
hundreds of species, including the milkweed-butterflies, 
the painted-beauty, the mourning- cloak (the first butter- 




INSECTS. 267 

fly to appear in the spring), and numbers of others, the 
catalogue of the names of which would 
prove dry reading. Only one needs 
more mention. This is the White 
Mountain butterfly, found only on the 
tops of the White Mountains, on the 
tops of the higher peaks of Colorado, 
and in Labrador. It is supposed that 
this form is a remnant of an Arctic 
fauna which extended over the north- 
ern United States when the country fig. 85.— White Mountain 
was covered by the great ice-sheet (see K terfly (a * neis semi ~ 
Geology), and on the retreat of the glacier these colonies 
were left stranded upon these points as the only places cold 
enough for them. 

Order IX. — Diptera (Flies). 

This order contains the true flies, and these forms are 
sharply marked off from other insects. The name means 
two-wings, and the flies have but a single pair of these 
organs, while on the metathorax is a pair of knobbed hairs, 
the so-called balancers (p. 237). The mouth-parts are 
fitted for sucking (fig. 86). The larva?, commonly known 
as maggots (fig. 87), are worm-like, lack feet, and in some 
species even lack a distinct head. In some the pupa is 
motionless, but in others, as in the mosquito, it has great 
powers of motion. The balancers are sensory organs, and 
they also serve as a means of maintaining the equilibrium, 
for if they be cut off from a fly, the animal can no longer 
direct its motions. 

The group of flies is very large in number of species, 
some being beneficial, while others are decided pests. 



268 



SYSTEMATIC ZOOLOGY. 



Among the former are those forms which feed upon other 
insects, as well as those which in their larval stages feed 
upon decaying organic matter. 

Most familiar of all is the common house-fly. This lays 
its eggs in horse-manure, each female producing about 





Fig. 86. — Head and proboscis of Fig. 87. — Larva (maggot) of house- 
blow-fly. After Kraepelin. e, eye ; fly. 
p, maxillary palpi. • 

150 eggs. In about ten to fourteen days these eggs become 
perfect insects, so that with this rapidity of multiplication 
it is no wonder that flies are abundant towards the end of 
summer. Allied to this is the blow-fly which lays its eggs 
in meat and other provisions. 

The bot-flies are parasitic in various domesticated ani- 
mals. These flies lay their eggs upon horses, cattle, or 
sheep, and the larvae enter the animal and cause serious 
injury or even death. The horse-bot larvae are taken into 
the stomach; the ox-bot or 'ox- warble' lives beneath the 



INSECTS. 269 

skin of cattle; and the sheep-bot enters the cavities con- 
nected with the nose or even the horns, producing the 
disease known as 'staggers/ 

More familiar are the mosquitoes, which lay their eggs 
on stagnant water. The larvae hatch out and are known 
as ' wrigglers.' They pupate beneath the surface, and 




Common house-fly {Mused). 



finally the perfect insect emerges to make itself an unmit- 
igated nuisance about our persons. Bad as the mosquitoes 
were long thought to be, the recent discovery that they 
convey to man the diseases yellow fever and malaria (p. 151) 
places them in the category of dangerous insects and has 
led to active efforts towards their extermination. Many 
proposals have been made for reducing the number of 



270 



SYSTEMATIC ZOOLOGY. 



these torments. The best is, possibly, the pouring of 
kerosene upon the surface of all stagnant water. This 




Fig. 89. — Larva (a) and pupa (&) of mosquito. 

will kill the eggs as they are laid, while it also destroys the 
perfect insects as they come from the water. 

Summary of Important Facts. 

1. The Arthropoda share with the Annelids a marked 
external and internal segmentation, expressed externally 
by the ringing of the body and the distribution of the 
appendages; internally by the chambering of the heart, 
the distribution of the ganglia, and, so far as they are 
present, by the arrangement of the tracheae. 

2. They are distinguished from the Annelids by the 
presence of jointed appendages, a pair to a somite, as well 
as by the unequal development of the somites, and by the 
grouping of the somites in regions. 

3. Three regions may be distinguished: a head with the 
parts concerned in sensation and the taking of food; a 
thorax, concerned in locomotion; and an abdomen, in 
which the primitive segmentation is most perfectly re- 
tained. 



INSECTS. 271 

4. By fusion of head and thorax, a cephalo thorax may 
be produced. 

5. The eyes are either ocelli or compound eyes. 

6. The abdomen may bear simple swimming-feet or it 
may lack distinct appendages. 

7. The Arthropoda are divided into Crustacea, Acerata, 
and Insecta. 

8. The Crustacea respire by gills. They have two pairs 
of antennae, usually two-branched feet; the reproductive 
ducts open near the middle of the body. 

9. The Crustacea are divided into Entomostraca and 
Malacostraca. The extinct Trilobites were near relatives 
of the Crustacea. 

10. The Acer ata lack antennae, they have a cephalo- 
thorax and abdomen, they respire by gills, lungs, or 
tracheae. The reproductive ducts open near the middle 
of the body. 

11. The Insecta have four pairs of appendages on the 
head; they breathe by tracheae, and the reproductive 
ducts open at the end of the body. 

12. The Insecta are divided into Chilopoda and Hex- 
apoda. 

13. The Chilopoda have numerous body-segments, each 
with a pair of legs, and with no distinction of thorax and 
abdomen. 

14. Chilopoda and Diplopoda are frequently united as 
a group of Myriapoda. 

15. The Diplopoda differ from Insecta in having a head 
with three pairs of appendages, most of the body-segments 
with two pairs of appendages, and the opening of the re- 
productive ducts in front of the middle of the body. 

16. The Hexapoda have the body divided into head, 
thorax, and abdomen. 



272 SYSTEMATIC ZOOLOGY. 

17. The thorax consists of three somites and bears three 
pairs of legs and usually two pairs of wings. 

18. The abdomen lacks distinct appendages. 

19. The head usually has a pair of compound eyes and 
three ocelli. The mouth-parts are either mandibulate or 
haustellate. 

20. Wingless insects usually have a direct development 
(Ametabola); winged insects may have an incomplete 
metamorphosis (Hemimetabola) , or a complete meta- 
morphosis (Holometabola). 

21. Classification of the Hexapoda is based on the char- 
acter of the metamorphosis, and the structure of the 
mouth-parts and the wings. 

22. The Hexapoda are divided into Thysanura, Orthop- 
tera, Pseudoneuroptera, Neuroptera, Coleoptera, Hymen- 
optera, Hemiptera, Lepidoptera, and Diptera. 



Phylum VI.— ECHINODERMA. 



The term Echinoderma means spiny skin, and both star- 
fishes and sea-urchins possess this peculiarity in a high 
degree. But besides this external characteristic there are 
many other features which dis- 
tinguish the group. In fact, 
there is scarcely a division in 
the whole animal kingdom more 
sharply marked off from other 
forms than this. In all the 
body is built on that radiate 
plan which is so prominent in 
starfish and urchin, and in all 
except a few starfish there are 
five rays, although in some 
the rays may subdivide. This 
radiate condition affects not 
only the external surface, but 
may extend to every system as T 

J J J Fig. 90. — Larva of a starfish, en- 

well. And yet we may trace in larged. m, mouth; », vent, 
every form a bilaterality, and development shows that the 
bilateral condition is primitive, for the larvae (see fig. 90) 
clearly have the two sides alike, while the radial symmetry 
of the adult only appears later in the growth. It was this 
radial arrangement of parts which formerly led to the union 
of Echinoderma and Ccelenterata as a branch Radiata. a 

273 




274 SYSTEMATIC ZOOLOGY. 

grouping which more accurate knowledge has shown to be 
untenable. 

Chief among the features marking off the two groups are 
the possession of a complete alimentary canal with mouth 
and vent, and of a large body-cavity (ccelom) distinct from 
the digestive tract. In a few cases, as in certain starfishes, 
the vent may be small or entirely closed, but the fact that 
in the larva the intestine opens to the exterior (Fig. 90, v) 
shows that the condition of the adult is the result of degen- 
eration. The large body-cavity or coelom is distinct from 
the other body-cavities in that it does not contain blood 
and is without connection with the cavities of the digestive 
tract and circulatory systems. 

The ambulacral system is also very characteristic. Its 
structure is rather complex (fig. 91), consisting of (1) an 
opening to the exterior either directly or by the inter- 
vention of a perforated calcareous plate, the madreporite; * 
(2) a stone-canal, connecting the madreporite with (3) a 
circular or ring-canal around the mouth. This stone-canal 
receives its name from the fact that its walls are usually 
strengthened by deposits of lime. From the ring-canal 
(4) a radial canal extends into each of the rays, giving 
off at regular intervals pairs of canals which connect, with 
the (5) ambulacra. These last consist of two parts, the 
ambulacra proper, which are on the outside, and the 
ampulla, which project into the ccelom. Both these 
structures are hollow and muscular, and the ambulacra 
each terminate with a sucker. By contraction the fluid 
of the ambulacral system is forced from the ampullae into 
the ambulacra, thus extending them, while contraction of 

* In the adults of most Holothurians the madreporite opens 
into the coelom, but in the larvae of these the opening is to the 
external world. 



ECHINODERMS. 



275 



the ambulacra forces the fluid back into the ampullae. 
The radial and ring canals serve to connect the various 
parts of the ambulacral system, but the functions of the 
madreporite and stone-canal are less certain. 

All of the echinoderms are characterized by the pres- 




Fig. 91. — Ambulacral system of a starfish, a, ampullse; ab, ambulacra; c, 
radial canal; m, madreporite; n, radial nerve; p, Polian vesicle; r. 
ring-canal; below it the ring-nerve; s, stone-canal; t, racemose vesicle, 

ence of calcareous plates in the skin, and in all except 
holothurians these plates are united into a more or less 
solid skeleton covered externally with a thin layer of 
skin. When this firm skeleton is developed various 
regions may be recognized, the most important being 
(1) ambulacral areas, through or between the plates of 
which the ambulacra protrude; (2) inter ambulacral areas, 
embracing a row of plates at either side of the ambulacral 
area, and (3) adambulacral, including the rest of the sur- 
face. The ambulacral areas mark the radii of the animal 
and the interambulacral are interradial in position. 

In all there is more or less capacity for regeneration of 
lost parts. Thus some of the holothurians can cast out 



276 SYSTEMATIC ZOOLOGY. 

the alimentary canal and re-form it, while the starfishes 
can reproduce lost arms. Hence starfishes with one or 
more arms much smaller than the rest are comparatively 
common. 

Reproduction is exclusively by means of eggs, and in 
the majority the young larva differs greatly from the adult, 
being bilaterally symmetrical and frequently provided with 
numerous long arms which may be soft or may be ren- 
dered rigid by an internal skeleton. The adult echino- 
derm forms on one side of the larva and gradually in- 
creases in size, absorbing the flesh of the larva in itself. 

All of the echinoderms are marine, and members of the 
phylum occur as fossils in the rocks of all ages from the 
Paleozoic to the present. The echinoderms are divisible 
into five classes. 

Class I.— ASTEROIDA (Starfishes). 

In the starfishes the flattened body is either pentagonal, 
or has a number of arms, or rays (usually five, sometimes 
twenty or more), giving it the shape of a star. The 
mouth is in the centre of the disc which unites the rays, 
and is always without jaws or other hard parts. In the 
body-wall are numerous calcareous plates, movable on 
one another. In the axis of each ray, on the side of the 
body with the mouth {oral surface), are regularly arranged 
ambulacral plates, margined on either side by correspond- 
ing interambulacral plates. In the rest of the surface 
{aboral surface) no such regularity of plates occurs. The 
mouth opens directly into a capacious stomach, the extent 
of which is increased by gastric pouches. The stomach 
is also partially divided by a constriction into two cham- 
bers, an oral, cardiac, and an aboral, pyloric, division. 



ECHINODERMS. 277 

From the latter a short intestine runs to the aboral pole, 
where it may open by a vent, but in some no vent 
occurs. Into the pyloric chamber empty the ducts of five 
pairs of glands (hepatic cceca) which secrete the digestive 
fluids, while from the intestine arise from one to five 
saccular outgrowths, the branchial trees, the function of 
which is uncertain. Retractor muscles serve to draw back 
the stomach after a meal (see below). 

The nervous system chiefly consists of a nerve-ring 
around the mouth and a radial nerve in each ray, the 
whole paralleling the water-vascular system. Eye-spots, 
one at the end of each ray, are the only specialized sense- 
organs present. 

The circulatory organs consist of a so-called heart 
beside the stone-canal, from which vessels run in various 
directions, the chief portion running between the nervous 
and water-vascular tracts. The only respiratory organs 
are the thin-walled branchiae, which are outpushings of 
the body-cavity upon the dorsal surface. 

The reproductive organs occur at the bases of the arms, 
one organ on either side of each ray, the ducts emptying 
in the angle between the arms. From the eggs there 
hatch out larvae (fig. 90), which are free-swimming and 
bilateral, and which show not the slightest trace of the 
radial shape of the parent. 

The starfishes are all marine. They feed largely on 
clams, oysters, and other molluscs, and are regarded as one 
of the greatest pests on oyster-beds. The way in which the 
starfish feeds is interesting. It has no hard parts to break 
the shell, while the mouth is too small to admit of swallow- 
ing the oyster. So it folds itself around its prey, attaching 
its ambulacra to the valves of the shell, and then begins 
to pull the valves apart. At first this has no effect, but 



278 



SYSTEMATIC ZOOLOGY. 



gradually the muscle of the oyster becomes fatigued, until 
at last it can no longer hold the shell closed. Then the 
starfish protrudes its stomach from the mouth, envelops the 
flesh of the oyster with it, and thus digests the oyster out- 
side of the body. The retractor muscles are to draw the 
stomach back after a meal. This method of external eat- 
ing explains the frequent degeneration or absence of 
intestine and anus (p. 277). 



Class II.— OPHIUROIDEA (Brittle-stars). 

The brittle-stars, or serpent-stars as they are frequently 
called, are much like the true starfishes, the chief distinc- 
tions being that in the brittle-stars the arms and the disc 
are sharply distinct from each other, and that the extremely 
mobile arms are long, slender, and somewhat snake-like. 
A little closer examination shows that the ambulacral 

groove has been carried into 
the interior of the arms, and 
that here one must search for 
the ambulacral plates (fig. 
93). There is no vent, and 
the madreporite occurs on 





-Brittle-star (Ophiopholis) 
From Morse. 



Fig. 93. — Cross-section of arm of 
brittle-star, a, ambulacral plate; 
ao, ambulacral opening. 



the lower side of the body, usually covered by one of the 
plates surrounding the mouth. There are a few forms in 
which the arms branch again and again, and since when 



ECHINODERMS. 279 

captured these forms bend the arms inwards towards the 
mouth, giving a somewhat basket-like appearance, these 
are known as 'basket-fish.' The name brittle-stars is due 
to the fact that in some the arms are very easily broken. 
A few brittle-stars produce living young. 



Class III.— CRINOIDEA (Sea-lilies). 

While all other echinoderms are free throughout their 
lives, the crinoids are characterized by being fixed to some 
firm support by a long stalk arising from the aboral surface 
of the body. In most the stalk persists throughout life, 
but in a few, after the adult condition is reached, the body 
separates from the stalk and thereafter follows a free life. 
From the central disc or calyx radiate the five (usually) 
branching arms, and chese arms and their branches bear 
small branchlets > go that as these animals rest in their 
ordinary position, the whole forms a funnel-like net with 
the mouth at the bottom (fig. 94). On the upper (oral) 
side of all these branches run grooves converging at the 
mouth (fig. 95), and so any object which falls anywhere 
on the funnel is brought to the animal as food. The ali- 
mentary canal runs spirally through the calyx (fig. 95), 
and the vent is on the oral surface. The stalk, like the 
calyx, is strengthened by calcareous plates, those of the 
stalk being disc-like and piled one on another. 

Crinoids, with the exception of the free forms (Comatula) , 
are among the rarities of museums, as they are found only 
in the deeper seas. In past time, however, they were very 
abundant, and whole layers of rock in certain localities are 
made up of their remains. The fossil forms present a 
greater variety of shape than do the living representatives. 



280 



SYSTEMATIC ZOOLOGY 



Class IV.— ECHINOIDEA (Sea-urchins). 

In the sea-urchins the body is spherical, heart-shaped, or 
disc-like, and the ambulacral areas extend, like meridians, 




Fig. 94. — Crinoid (Pentacrinuf), half 
natural size. From Brehm. 



Fig. 95.— Mouth area of a crinoid 
(Comatula), showing the course of 
the intestine leading from the 
mouth (m) to the vent (a), g, 
grooves leading from arms to mouth. 



from oral to anal regions. In short, sea-urchins are easiest 
compared with starfishes, if we imagine the arms of the 



ECHINODERMS. 281 

latter bent backwards until they meet above. In this way 
the terminal eye-spots * would be brought next to the anal 
area, while by the union of the arms the reproductive open- 
ings would be forced into a position between the ocular 
plates, and the madreporite would become pressed against 
one of the reproductive (genital) plates. 

All of the plates are firmly united to one another, while 
the spines are freely movable, and share, with the ambu- 
lacra, locomotor functions. The mouth is armed with five 
teeth, and to aid in the movement of these a calcareous 
framework is found just inside the mouth, known from its 
first describer as Aristotle's lantern. In some, as in our 
common urchins, this framework and its muscles are com- 
plicated. From the mouth the tubular alimentary canal 
pursues a winding course (usually folding on itself) to the 
vent. Hepatic caeca, gastric pouches, and branchial trees 
are lacking. The reproductive organs become fused into 
five lobes by the union of those of the same interradius. 

The Echinoidea are divided into three orders: 

Order I. — Regularia. 

In these, which embrace the more common urchins, the 
mouth is at one pole, the vent at the other, and the body 
is approximately spherical. 

Order II. — Clypeastroidea (Sand-cakes). 

In the 'sand-cakes' and 'sand-dollars' we have urchins 
in which the test is disc-shaped and the ambulacra are con- 
fined to the upper surface. The mouth is in the centre of 

* In only a few sea-urchins are the 'eye-spots' known to be 
visual organs; the opening in the ocular plate is for the passage 
of the terminal tentacle of the ambulacra! system. 



282 



SYSTEMATIC ZOOLOGY. 



the lower surface; the vent is on the margin of the disc, 
or near the margin on the lower surface. It is interradial 
in position. Comparisons with forms like these, or better 




A B a 

Fig. 96. — A, oral, and B, aboral surfaces of sand-dollar (Echinarachnius). a, 
vent; g, genital pores; i, ambulacral areas; m, madreporite ; o, mouth. 

with Spatangoids (infra), show why the odd or unpaired 
ray of a starfish is called the anterior ray (see Laboratory 
work). In a few of the sand-cakes the margin of the disc 
is notched, while in others there may be perforations ex- 
tending through from upper to lower surface. 

Order III. — Spatangoids (Heart-urchins). 

In these the body, flat below, arched above, has a heart- 
shaped outline, and both mouth and vent are eccentric in 
position upon the lower surface. The ambulacra are all 
on the upper surface, but the anterior row is lacking. 



Class V.— HOLOTHURIDEA (Sea-cucumbers). 

The Holothurians are cylindrical Echinoderms, with 
mouth and vent at the ends of the body, and usually with 
the ambulacra scattered over the surface in such a way as 
to make the comparison with a cucumber most apt. Around 



ECHINODERMS. 



283 



the mouth is a circle of tentacles (in reality enormously 
developed ambulacra), and with these the animals obtain 
their food, which consists of small organisms living in the 
sand and in some instances of decaying animal matter. 




Fig. 97. — Sea-cucumber (Cucumaria frondosa). From Emerton. 



Inside, the pharynx is surrounded by calcareous plates, the 
whole resembling slightly the lantern of the sea-urchin, 
but no teeth are ever developed. In most species the 
madreporite is inside the body, and in many the branchial 
trees (p. 277) become developed into large tree-like struc- 



284 SYSTEMATIC ZOOLOGY. 

tures. Along our shores two groups or orders occur: 
Pedata, in which there are ambulacra and branchial trees; 
and Apoda, in which both these structures are lacking, 
and the body is decidedly worm-like. 

The food of the holothurians consists largely of organic 
matter in the sand or mud on which they live. The ten- 
tacles are used to push the sand into the mouth. 

Summary of Important Facts. 

1. The Echinoderma have a calcareous integument in 
which spines are frequently developed. They have both 
radial and bilateral symmetry, the latter primitive. All 
are marine. 

2. They have a complete alimentary canal, with both 
mouth and vent, distinct from the large body-cavity. 

3. They have an ambulacral system consisting of madre- 
porite, stone-canal, ring-canal, radial canals, ampulla?, and 
ambulacra. In many this serves for locomotion. 

4. The body surface can be divided into ambulacral, 
interambulacral, and adambulacral areas. 

5. The Echinoderms possess marked powers of regener- 
ating lost parts. 

6. They reproduce solely by means of eggs. The young 
undergo a metamorphosis in reaching the adult condition. 

7. The Echinoderma are divided into Asteroidea, Ophiu- 
roidea, Crinoidea, Echinoidea, and Holothuridea. 

8.. The Asteroidea are star-shaped, without marked dis- 
tinction between rays and disc; the radial canals and 
nerves are external to the calcareous ambulacral plates. 

9. They are very destructive to molluscs. The stomach 
is protruded from the body in order to digest the prey. 

10. The Ophiuroidea differ from the Asteroidea in 



ECHINODERMS. 285 

having the disc distinct from the rays, and the radial 
canal and nerve inside the calcareous wall of the rays. 

11. The Crinoidea are fixed by an aboral stalk during a 
part or a whole of their life. The arms, which may branch, 
radiate from a central calyx which contains the alimen- 
tary canal. The mouth is uppermost and at the bottom 
of a funnel formed by the arms. 

12. The Echinoidea have a spherical, disc-like, or 
heart-shaped body, the ambulacral areas appearing as 
meridians on its surface. The radial nerves and canals 
are inside the calcareous plates. 

13. The mouth is surrounded by a complicated jaw 
apparatus (Aristotle's lantern). 

14. The Holothuroidea are elongate and cylindrical, 
with mouth and vent at the ends; there is no Aristotle's 
lantern; the madreporite is usually internal. 



Phylum VII.— CHORD ATA. 

The group of Chordates has been formed from animals 
taken from other divisions and united with the Vertebrates. 
The Tunicata were formerly classed as Mollusc a, the Enter- 
opneusta as both Echinoderms and Worms. Yet when all 
these are studied more accurately, they are seen to have 
three important characteristics which are common to all 
and which mark them off sharply from all other phyla. 
These features are: (1) the possession of gill-slits; (2) a 
nervous system lying wholly on one side of the alimentary 
canal; and (3) a notochord which has given the name to 
the phylum. 

Gill-slits are pockets in the sides of the gullet or pharynx 
which lead from the throat to the exterior. Blood-vessels 
run in the partitions between the slits, sending fine branches 
to the gills, which are usually developed on the sides of 
the slits. 

The notochord is a gelatinous skeletal structure, cylin- 
drical in shape, which lies between the alimentary canal 
and the central nervous system. In the lower groups it 
forms the sole skeleton; in the vertebrates it is more or 
less completely replaced by the vertebral column, to be 
described below. 

There are four divisions of the Chordata, only three of 
which need description here: Tunicata, Leptocardii, and 
Vertebrata. 

286 



TUNIC ATES. 287 



Branch I.— TUNICATA. 

The fact that these forms had any relationship to the 
Vertebrates would never have been suspected had one 
studied only the adults. When 7 however, the development 
was studied, it was perceived that these forms had larvae in 
which there was a notochord, gill-slits, and a nervous system 
much like that of the Vertebrates; in short, that in shape 
and in structure these young Tunicates were decidedly 
tadpole-like. Then these tadpoles settled down upon some 
object and passed through a metamorphosis in which the 
tail was lost, the nervous system was contracted into a 
mass, and the body became more or less saccular and 
covered with an external envelope or 'tunic/ which gives 
the name to the group. 

Of these Tunicates there are many varieties, but the 
essential features of the adult can be made out from the 
generalized figure given. The body is globular, and shows 
two openings on the outside. One of these is the mouth, 
which communicates with a pharynx or gill-region per- 
forated by numerous gill-slits. At the bottom of this 
pharyngeal region is the oesophagus, which leads to stomach 
and intestine, the latter twisting so as to terminate at the 
bottom of a cloacal chamber, which opens to the exterior 
by the other aperture mentioned. The water, which passes 
through the gill-slits, is collected, and passes into the same 
cloacal chamber. The nervous system consists of a centre 
or ganglion between the two openings, from which nerves 
radiate to the various parts. There is a heart at the 
opposite side of the body, and a peculiarity of this organ 
is that it regularly changes in its action, the blood flowing 



288 SYSTEMATIC ZOOLOGY. 

in a direction opposite to that which it followed a moment 
before. 

The species of Tunicates are numerous, and show great 
variety of form. A characteristic of many is the power to 
reproduce by budding, and as a result there are formed 




Fig. 98. — Diagram of a Tunicate, o, branchial chamber, perforated by gill- 
clefts, and connecting at the bottom with the oesophagus, which leads to the 
globular stomach, and thence by the intestine to the vent, v; h, heart; n, 
nervous system.; m, mouth. 



large colonies, the members of which are more or less inti- 
mately connected with each other. In some cases the 
animals resulting from budding produce eggs, and these 
eggs grow into forms unlike their parents, but like those 
from which the parents were budded. In other words' 



LANCELETS. 



289 



the child does not resemble the parents, but the grand- 
parents, another example of alternation of 
generations. 

The Tunicates are all marine, and they 
abound in the seas of all parts of the world. 
Some of them are known from their shapes 
and color as 'sea-peaches/ others as 'sea- 
pears/ while a common name for all is ' sea- 
squirts/ due to the fact that they squirt water from the 
openings upon being disturbed. 




Fig. 99. — A simple 
Tunicate (Molgula 
manhattensis). 



Branch II.— LEPTOCARDII (Lancelets). 

The few species of lancelets (Amphioxus) are all marine 
and occur in warmer seas. They have a body which is 
fish-like, but they differ from all fishes in the absence of a 
true heart and of a skull. The gill-slits are numerous 




Fig. 100. — Diagram of Amphioxus (after Hertwig and Boveri). Above (dotted) 
is the nervous system; below it (cross-lined), the notochord; the mouth is 
surrounded by the circle of tentacles; below the notochord is the region of 
gill-slits; the vent is near the posterior (right) end below. 



(about sixty), and these empty into a gill-chamber recall- 
ing in some features that of the tadpoles. The notochord 
runs the whole length of the body, and a stomach is lack- 
ing, the liver emptying into the intestine just behind the 
gills. Limbs or paired fins are absent, but there is a 
median fin at the end of the body. The animals are about 
two or three inches long, are almost perfectly transparent, 
and bury themselves in the sand, only the mouth end, 



290 SYSTEMATIC ZOOLOGY. 

encircled by a fringe of delicate filaments, appearing above 
the surface. They are without any economic importance, 
but their extremely simple structure makes them intensely 
interesting to the naturalist. 

Branch III.— VERTEBRATA. 

All of the forms associated together as a group or branch 
— Vertebrata — receive this name, since they all possess a 
'back-bone' composed of separate bones or vertebras. This 
one character of itself would hardly warrant this group- 
ing, especially since some have the vertebras but feebly 
developed, while in other features they are closely similar 
to those with a well-developed back-bone. This presence 
of vertebras is closely associated (correlated) with other 
features of equal or even of more importance, and it is this 
totality of similarity that justifies the group. 

All vertebrates have an inner supporting skeleton, and a 
few forms, like the turtles, have in addition an external 
skeleton derived from the skin. The internal skeleton, for 
convenience of treatment, may be divided into one portion 
lying in the axis of the body, and a second portion pertain- 
ing to the limbs and appendages. Besides these there is 
a third part, the visceral skeleton, developed in connection 
with the jaws and gills. 

The axial skeleton consists of the vertebral column (back- 
bone), the skull, and the ribs. In all vertebrates, at least 
in the young stages, a solid rod of gelatinous tissue runs 
through the body between the central nervous system and 
the alimentary canal. In front it terminates near the 
middle of the brain ; behind it runs to the end of the body. 
This rod is the .notochord. In the higher vertebrates it 
disappears long before the animal becomes adult; but in 



VERTEBRATES. 291 

the lower, as in the sharks, it can be recognized through- 
out life. This notochord is enveloped in a membranous 
notochordal sheath, and in this sheath are formed rings of 
cartilage which give rise to the bodies (centra) of the verte- 
brae. Between these rings no cartilage is formed and hence 
the whole column is jointed and flexible. In the sharks 
these rings and other parts of the skeleton remain carti- 
laginous ; in other vertebrates any or all may be converted 
into bone. In a typical vertebra, for instance, in the tail 
of a fish (fig. 101, A), outgrowths from the centrum occur 




Fig. 101. — Different vertebrae and connected structures. A, in tail region of 
teleost; B, in body region of teleost; C, in tail region of salamander; D, in 
mammal; c, centrum; h, haemal arch (rib in B); n, neural arch; r, rib; s, 
sternum; t, tran verse process. 

above and below, forming two arches. The upper of these 
(neural arch, n) encloses the spinal cord, the lower (hamial 
arch, h) extends around the blood-vessels of the tail. 
Farther forward, in the trunk region of the bony fish, the 
two halves of the haemal arch do not meet below, but form 
slender threads (ribs, B, h) which support the flesh around 
the viscera. In the forms above the fishes an outgrowth 
(transverse process, C, D, t) may rise on either side of the 
vertebral centrum, and the ribs, when they occur, are con- 
tinuations of these transverse processes, and have nothing 



292 



SYSTEMATIC ZOOLOGY. 



to do with the haemal arches. Hence it follows that the 
ribs in a fish and those in a higher vertebrate — a bird or 
man, for example — are not identical; i.e., are not homol- 
ogous. The centra of the vertebras may be hollow at either 
end (amphicoelous) , as in fishes, or they may be hollow 
behind and rounded in front (opisthoccelous) , as in the sala- 
manders ; or again, they may be hollow in front and convex 
behind (procoelous) , as in many reptiles; or lastly, they may 
have flat surfaces, as in most mammals. 

The vertebral column is capable of division into regions. 




Fig. 102. — Diagram of the skeleton of a mammal, showing regions of vertebral 
column, etc. d, cervical; e, thoracic; /, lumbar; g, sacral; h, caudal verte- 
brae; i, scapula; k, humerus; I, radius; m, carpus; n, ulna; o, metacarpus; 
p, pelvis; r, femur; s, fibula; t, tibia ; u , tarsus ; v, metatarsus; w, phalanger ; 
y, sternum. 



In the fishes there are two of these, trunk and caudal, the 
former being distinguished by bearing ribs. In the Am- 
phibia a cervical region is distinguished from the trunk by 
the absence of transverse processes from its single vertebra, 
while the caudal is separated from the trunk by a sacral 



VER TEBRA TES. 293 

region, the vertebra of which is connected with the bones 
(girdle) supporting the hind limbs. In the higher verte- 
brates the trunk vertebra can be divided into thoracic 
and lumbar regions, the former with, the latter without, 
ribs. 

As we have just seen, there may be two kinds of ribs— 
those of fishes and those of the higher 
vertebrates. In reptiles, birds, and mam- 
mals the ribs of one side fuse at their ven- 
tral ends with their fellows of the opposite 
side. The fused regions separate from the 
ribs and unite together, giving rise to the 
breast-bone or sternum (fig. 103). In 
some sterna the separate elements can be 
traced; in others the fusion is complete. 
The sternum in the Amphibia has no con- 
nection with the ribs, and may therefore 
be different from the breast-bone in the 
Sauropsida and Mammalia. 

The skull consists of two portions: the 

. . , . r . Fig. 103. — Ster- 

cranium and the face, or better, the vis- numofdog.show- 
ceral skeleton. The former affords pro tec- elements of which 

. , ' , it is composed. 

tion to the bram and support to the organs 

of sense; the visceral portions cluster around the mouth, 

nose, and throat. 

In the sharks the cranium is a continuous box of carti- 
lage, only perforated for the passage of nerves and blood- 
vessels. In the other vertebrates some or all of this carti- 
lage becomes replaced by bone, either by direct conversion 
(ossification) or by substitution. The bony cranium (un- 
like the cartilaginous cranium) is not a continuous wall, 
but is composed of separate bones firmly united together, 
the number varying between wide limits, being most 




294 SYSTEMATIC ZOOLOGY. 

numerous in the lower and reduced by fusion or actual 
loss in the higher forms. 

In the sharks the visceral skeleton is very simple, being 
represented by the upper and lower jaws (Fig. 104, pq, m) 
by the gill-arches or giil-bars, and by a few cartilages sup- 
porting the lips. The upper jaw is not firmly united to 



OXEEE3; 




Fig. 104. — Diagram of the skull and branchial arches of a shark, h, hyoid; 
hm, hyomandibular, forming the suspensor of the lower jaw, m (Meckel's car- 
tilage); pq, upper jaw (pterygoquadrate); s, spiracle; I-V, gill-arches, 
between which are shown the gill-clefts. 

the cranium, but is held in position by muscles and liga- 
ments, and by the hyomandibular (hm), while the lower 
jaw is hinged to the upper, and not to the cranium. Com- 
parisons, which cannot be described here, show that the 
upper jaw of the shark is not the same as the upper jaw 
in the other vertebrates. In them numbers of other bones 
are added to the skull, and the upper jaw of the shark is 
only comparable to two pairs of bones, known to anato- 
mists as the pterygoids and the quadrates (fig. 105), 
hence the name pterygoquadrate cartilage used for this 
part in the sharks. 

The rest of the visceral skeleton consists of bars of 
cartilage on either side of the throat between the gill- 
slits, the series being united below (Fig. 104). These gill- 
arches serve to keep this region, weakened by the openings, 
from collapse. The most anterior of these gill-bars has 
the special name of hyoid (Fig. 104, h), and its upper part 



VERTEBRATES. 



295 



that of hyomandibular. There is much evidence tending 
to show that the lower jaw and the ptery go quadrate bar 




Fig. 105. — Skull of cod. (After Hertwig.) The dotted portion is the pterygo- 
quadrate arch and is equivalent of the upper jaw of the shark (Fig. 104), 




Fig. 106. — Diagram (after Wiedersheim) showing the relation of permanent 
structures (dark) to the gill-arches of the embryo (dotted), h, hyoid arch; 
I, cartilages of larynx; I, II, III, gill-bars. At the front of h and I is shown 
in black the hyoid bone of the adult, with its two horns; behind the ear, at 
the other end of the hyoid arch, is (black) a piece (styloid process) which 
joins the skull. 



are but modified gill-bars. With the disappearance of 
gills in the higher vertebrates the branchial arches tend 



296 SYSTEMATIC ZOOLOGY. 

to disappear, and in birds and mammals only parts of 
the hyoid and first gill-bar remain in the adult, where 
they are largely employed as supports for the tongue 
and larynx (fig. 106). 

There are never more than two pairs of appendages in 
the vertebrates. These are the fore and hind limbs. In 
their skeletons these are much alike, and in each can be 
recognized arches of bone (girdles) uniting the limb to the 
trunk, and the skeleton of the limb proper. These girdles 
are known respectively as the shoulder, or pectoral, and 
the pelvic girdle. In the fishes the girdles are simple 
arches, and the skeleton of the limbs is largely composed 
of fin-rays to support the flattened swimming-organ. 

In those vertebrates which support the weight of the 
body upon the limbs the appendicular skeleton is more 
complicated. In its typical condition the shoulder-girdle 
consists of three bones, which meet * to afford attachment 
for the skeleton of the fore limb. One of these bones, the 
shoulder-blade (scapula), is dorsal. It never joins the 
vertebras, but is united to the trunk by muscles and liga- 
ments. The other two extend ventrally from the shoulder- 
joint and meet the sternum. Of these the anterior is the 
collar-bone (clavicle), the posterior the coracoid. 

In the pelvic girdle there are likewise three bones, which 
at their point of junction give rise to the hip-joint. The 
dorsal bone is the ilium, which articulates with the sacral 
vertebras (p. 292), while below are found the ischium and 
pubis, the latter being the more anterior. Ischium and 
pubis unite with their fellows of the opposite side, thus 
completing the arch. 

In the pelvic girdle the parts mentioned are pretty con- 

* The clavicle frequently does not enter into the formation of the 
shoulder-joint. 



VERTEBRATES. 297 

stant, but in the shoulder-girdle other bones may be added, 
or either coracoid ; or coracoid and clavicle may disappear. 
In the birds the clavicles unite, forming the wish-bone 
(furcula) . 

The bones of the fore limb (fig. 107) are: a single bone 
(humerus) in the arm; two bones (ulna and radius) side 




Fig. 107.--Diagram of fore and hind limbs of a terrestrial vertebrate, with one 
half of their girdles, c, carpus; cl, clavicle; co, coracoid; /, fibula; e, femur; 
h, humerus; il, ilium; is, ischium; mc, metacarpus; mt, metatarsus; p, 
pubis; r, radius; s, scapula; t, tarsus; u (in upper) ulna, (in lower) tibia; 
1-5, digits, each composed of phalanges. 

by side, in the forearm; a series of nine bones (carpals) 
in the wrist; five longer bones (metacarpals) in the palm; 
and several rows (phalanges) of five bones in the digits. In 
the hind limb the conditions are closely similar: a single 
femur in the thigh, tibia and fibula in the shank, nine 
tarsals in the ankle^ five metatarsals succeeding these, and 
finally the phalanges of the toes. 

These are the typical numbers, but they may be reduced 
through disappearance or fusion, and this reduction usually 
appears first in the toes, and may proceed so far, as in the 
horse, that one toe alone remains functional. 

The nervous system consists of a central and a periph- 
eral portion, the latter consisting of nerves going from 
the central system to all parts of the body. To these 
should be added the organs of general and special sense. 




298 SYSTEMATIC ZOOLOGY. 

The central system consists of an anterior brain, passing 
behind into the spinal cord. The brain is contained in the 
cranium; the spinal cord passes through the tube formed 
by the neural arches of the vertebrae. 

The spinal cord (fig. 108) is somewhat cylindrical, ta- 
pering behind, and contains in its centre a small canal. 

Nerves arise from the cord 
in pairs in regular sequence, 
and pass out between the 
vertebrae to all parts of the 
body and to the limbs. 
Fl ? P ini? 8 c^d Dia ^dor a sai c nTv^oot • Ea <* of these spinal nerves 

?oof^ y , Xte er matt;r Ventml ^^ h ^ two places of origin 

(roots) from the cord — one 
near the dorsal, the other near the ventral surface, but 
after a short course these roots unite into a common 
trunk. These roots differ greatly in structure and func- 
tion. The dorsal root bears a nervous enlargement or 
ganglion; the ventral has no such structure. Experiment 
shows that the dorsal root is concerned in bringing sensa- 
tions to the central nervous system, and, if it be cut, the 
parts to which it goes will be without feeling. The ven- 
tral root, on the other hand, is motor; i.e., it controls the 
action of muscles, glands, etc. If this root be cut, the 
parts which it supplies are paralyzed. Hence we may 
speak of the dorsal roots as afferent, since they bring sensa- 
tions to the central nervous system; while the ventral 
roots are efferent, because they carry nervous impulses in 
the opposite direction. 

The brain must be recognized as an enlarged and special- 
ized portion of the central nervous system. The canal of 
the spinal cord continues into the brain, enlarging there 
into four or more cavities or ventricles, connected by 



VERTEBRATES. 



299 



narrower portions. In the brain five divisions may be 
distinguished. Beginning in front, these are:* (1) the 
cerebrum, composed of right and left halves or hemi- 
spheres, and containing in their interiors the first and 
second ventricles; (2) the smaller 'twixt-brain, with thin 




Fig. 109. — Diagram of vertebrate brain, c, cerebrum; cb, cerebellum; h, in- 
fundibulum; m, medulla; o, olfactory nerve; ol, optic lobes; s, spinal cord; 
1-4, ventricles. 



walls and enclosing the third ventricle; (3) the thick- 
walled optic lobes; (4) the cerebellum; (5) the medulla oblon- 
gata, the fourth ventricle being contained in cerebellum and 
medulla. In the lower vertebrates these five regions are 
nearly equal in size, but the higher we go in the scale the 
larger proportionately do the cerebrum and the cerebel- 
lum become, until in man the cerebrum weighs about 
nine tenths of the whole brain. 

From the brain are given off, typically, twelve pairs of 
nerves, which are spoken of both by numbers and by 
their proper names. The majority of these are unlike 
the spinal nerves in that they have but a single root, and 
are correspondingly either sensory or motor. Thus the 
first or olfactory nerve, which goes to the nose; the second 

* Other names are frequently applied to these parts, as follows: 



Cerebrum, 
'Twixt-brain, 
Optic Lobes, 
Cerebellum, 
Medulla, 



Prosencephalon, 
Thalamencephalon , 
Mesencephalon , 
Metencephalon, 
My elencephalon , 



Parencephalon, 

Diencephalon, 

Midbrain, 

Epencephalon, 

Metencephalon. 



300 SYSTEMATIC ZOOLOGY. 

or optic nerve, to the eye; the eighth or auditory nerve, 
distributed to the ear, — are purely sensory. On the other 
hand, the third, fourth, and sixth {oculomotor, trochlearis, 
and abducens) nerves go to the muscles of the eye; the 
eleventh * (accessorius) goes to the muscles of the shoulder- 
girdle ; and the twelfth (hypoglossal) goes to the muscles of 
the tongue. These nerves are purely motor, but it must 
be remembered that the twelfth in the young of a few 
forms has a dorsal ganglionated root. The remaining 
nerves are like the spinal nerves in so far as they have 
both sensory and motor functions. The fifth or trigem- 
inal supplies the sense-organs of the head and the princi- 
pal muscles of the jaws. The seventh (facial) goes to 
the superficial facial muscles, and in the lower vertebrates 
supplies certain sense-organs (lateral-line organs) in the 
skin, but in man has lost its sensory functions. The ninth 
(glossopharyngeal) goes to the tongue and pharnyx; while 
the tenth (vagus or pneumogastric) supplies the sense- 
organs of the gill-slits and of the lateral line (below) of 
the trunk and sends branches to the stomach, lungs, gills, 
heart, etc. It will thus be seen that the vagus nerve cf 
the lower vertebrates is more than the pneumogastric of 
the terrestrial forms. 

Connected with the nervous system are the sense-organs. 
The skin contains small touch or tactile organs connected 
with afferent nerves, and these are for the recognition of 
pressure and temperature. Possibly allied to these are 
the organs of the lateral line, which are found only in the 
aquatic Ichthyopsida. These organs are sometimes free 
on the surface, sometimes in pits, while not infrequently 
the pits are connected by canals running beneath the 
surface, with openings to the exterior here and there. 
* This occurs in no ichthyopsidan vertebrate. 



VERTEBRATES. 



301 



This line of organs is plainly seen on the side of the body 
in most fishes. On the head, however, it frequently 
branches greatly and becomes enormously extended in 
this way. The occurrence of these structures in aquatic 
forms only would suggest that their function is connected 




Fig. 110. — Diagram of cranial nerves, a, alveolaris nerve* 6, buccalis nerve; 
c, cerebrum; cb, cerebellum ; ct, chorda tympani; e, ear; er, external rectus 
muscle; /, inferior rectus muscle; g, Gasserian ganglion; h, hyoid cartilage; 
hm, hyomandibular cartilage; hmd, hyomandibular nerve; i, internal rectus 
muscle; io, inferior oblique muscle; j, Jacobson's commissure; I, lateralis 
branch of vagus nerve; to, mouth; toc, Meckel's cartilage; md, mandibularis 
nerve; mx, maxillaris superior nerve; n, nose; o, optic lobes; op, ophthal- 
micus profundus nerve; os, ophthalmicus superficialis nerve; p, pinealisjp?, 
palatine nerve; po, posttrematic branch; pn, intestinal (pneumogastric) 
nerve; pr, pretrematic branch; ptq, pterygoquadrate cartilage; s, spiracle; 
so, superior oblique muscle; sr, superior rectus muscle; t, 'twixt-brain ; 
I-X, cranial nerves; 1-5, gill-slits. 

with that element; but what that function is, is not well 
understood. 

The taste-organs are within the mouth, principally on the 
tongue. They are poorly developed in some vertebrates, 
better in others. 

The olfactory organs are always placed in front of the 
mouth. They consist of a membrane folded so as to ex- 
pose a great amount of surface, and this surface is covered 
with the sensory structure, connected with the ends of the 
olfactory nerve, In the fishes the sacs containing this 



302 



SYSTEMATIC ZOOLOGY. 



membrane have only external nostrils, but in all others 
they are placed at one side of a tube, which leads from the 
external nostril to the back part of the mouth. Hence a 





Fig 

tebrates 



111. — Relations of the olfactory organ. A 
b, bn 
surface is folded 



b, brain; i, internal nostril; n 



!f 



in fishes; B, in higher ver- 
external nostril. The sensory 



fish can perceive odors in the water only as it swirls in and 
out of the nasal sac. In the air-breathing forms, odors in 
the air are drawn with the breath over the sensory surface. 
The essential part of the ear, the inner ear (fig. 112), con- 
sists of a thin membranous sac on either side of the head. 
s In three places this sac 

is so pinched as to form 
small tubes (semicircular 
canals) open at either end 
into the main chamber. 
The whole is filled with 
fluid in which are nu- 
merous minute solid par- 
ticles (otoliths). At one 

Fig. 112. — Diagram of mammalian ear. c, i r "u j. "U „ J « + 

cochlea; e, Eustachian tube; s, semicir-end 01 each tube and at 
cular canals, connected with the central -. * +Vi „ ro 

sac and separated from the surrounding places in tUe Sac are 
bone (black) by a space; t, tympanic , ■, 

cavity closed externally by membrane, and SenSOiy Organs Connected 
traversed by a bone, which conveys the .,, ,, -,., 

sound-waves to the inner parts. With the auditory nerve. 

Sound-waves entering the 
ear set the fluid in motion, causing the otoliths to strike 
the sensory organs and thus to stimulate the nerve. 




VERTEBRATES. 303 

In the sharks this ear-sac is placed behind and medial 
to the spiracle (p. 308). In the higher vertebrates the 
spiracle becomes closed on the outside, but the rest of the 
structure remains, and is known as the Eustachian tube, 
and as its outer end comes between the ear and the external 
world, one or more bones usually extend across the tube 
to convey the sound-waves to the sac. This forms the 
middle ear. In the frogs the outer end of the Eustachian 
tube is closed by the large tympanic membrane on the side 
of the neck. 

In the higher vertebrates an external ear occurs. This 
consists of a tube leading inward to the tympanic mem- 
brane, and to this tube are frequently added structures to 
catch and reflect the sound-waves into the tube. It should 
be mentioned that the ear is more than an organ of hearing ; 
it is also an organ for maintaining the balance, for if the 
ear or the auditory nerve be injured the animal can no 
longer maintain its equilibrium. 

The eye (fig. 113) is built on the plan of a photographic 
camera. The essential parts are a lens which brings the 
rays of light to a focus on the retina, and means for causing 
the image on the retina to stimulate the optic nerve. To 
these are added various accessory structures for protection, 
for regulating the amount of the light, etc. In the lower 
forms eyelids are absent, but higher in the scale folds of flesh 
are developed which can close over the organ. Many ani- 
mals have three of these eyelids, two working. vertically, 
the third, the nictitating membrane, drawn from the inner 
angle of the eye over the transparent cornea. This nictitat- 
ing membrane occurs in the eye of man as a small fold 
(semi-lunar fold), which has entirely lost its primitive 
protective function. 

Over the whole globe of the eye is a tough layer, the 



304 SYSTEMATIC ZOOLOGY. 

sclerotic coat, which is usually white (the white of the eye 
is part of it), and which may be cartilaginous or may 
even have bone deposited in it, as in many reptiles and 
birds. In front this layer becomes perfectly transparent, 
and is there known as the cornea. Inside of the sclerotic 
is found a densely black layer (choroid), and still within 
this the transparent retina, the outer portion of which is 



Fig. 113. — Diagram of vertebrate eye. c, choroid! &5ris; J.lens; n, opticnerve; 
r, retina; s, sclerotic. 

imbedded in the choroid. In front the choroid is con- 
tinued into the iris, & circular muscle with an aperture, 
the pupil, in its centre. This iris, which is colored, regu- 
lates by its enlargement and contraction the amount of 
light which is admitted to the visual parts of the eye. 
Back of the iris, and held in position by a circular muscle 
and ligament, is the transparent lens. In front of this 
lens is a watery fluid (aqueous humor), while behind it and 
between it and the retma is the somewhat denser vitreous 
humor. 

The optic nerve enters the eye from behind, passing 



VERTEBRATES. 305 

through sclerotic, choroid, and retina, and is then distrib- 
uted over the inner surface of the latter layer. 

The eyeball is moved by six muscles, which are essentially 
alike in all vertebrates. Four of these are straight or 
rectus muscles, two are oblique. These muscles are con- 
trolled by the three eye-muscle nerves (p. 300). 

The alimentary canal runs through the body from mouth 
to vent. In it several parts can be distinguished. 

The mouth, at or near the anterior end, is without 
fleshy lips, except in the mammals. The mouth is fre- 
quently armed with teeth, and even in those groups, like 
the turtles and the birds, where teeth are absent the 
germs occur in the young, a fact which points to the 
descent of these from toothed ancestors. 

The tongue is formed as a fold of the floor of the mouth, 
and is usually supported by a skeleton (hyoid bone, p. 
294) derived from the first or first and second visceral 
arches. In some it is without powers of motion, but 
frequently it is very mobile. Usually it is attached 
behind, the front margin being free, but in many Am- 
phibia it is attached in front and folded back in the mouth. 

The mouth-cavity is succeeded by the pharynx, a re- 
gion concerned in respiration and distinguished by contain- 
ing the respiratory openings (internal nostrils, gill-slits, 
glottis). 

Behind the pharyngeal region is the digestive tract 
proper. In some vertebrates it is scarcely possible to dis- 
tinguish regions in it, but in most cases several distinct 
portions occur. Those usually to be recognized are the 
following : 

The pharynx communicates with the gullet or (Esopha- 
gus, a muscular tube which frequently serves only to 
carry food back to the stomach. On the other hand, a 



306 SYSTEMATIC ZOOLOGY 

part of this tube may be expanded into a glandular food- 
reservoir or crop (birds). 

In some fishes and Amphibia the stomach is hardly 
differentiated from the oesophagus, but in other forms it 
is well developed, with muscular and glandular walls. It 
may even be divided into several portions. Thus in 



Fig. 114. — Diagram of the digestive tract of a mammal, b, brain; d, dia- 
phragm; h, heart; i, intestine; k, kidney; I, liver; o, oesophagus; p, pan- 
creas; s, stomach; sp, spleen; v, vent. 



birds (fig. 147) we frequently find two parts, one chiefly 
glandular, while the other {gizzard) is extremely muscu- 
lar. In the ruminants (p. 385) the specialization is 
carried farther, and we find four divisions to the or- 
gan. 

While some absorption of food takes place in the stom- 
ach, the intestine is the chief absorptive portion of the 
alimentary canal. In some vertebrates it is short and 
straight, in others long and convoluted, there being usu- 
ally a correlation between length of intestine and the 
character of the food, this region being longer in the 
vegetable feeders. Increased absorptive surface is ob- 
tained in several ways, in addition to lengthening of the 
intestine. In the lower Ichthyopsida this is accomplished 



VERTEBRATES. 307 

by the development of an extensive internal fold (spiral 
valve). In others there are numerous small longitudinal 
folds, while in the highest vertebrates transverse folds 
occur on which are minute finger-like outgrowths {villi). 
In the lower vertebrates the hinder part of the intestine 
receives the ducts of the excretory and reproductive 
organs, and at such times is called a cloaca. In the 
mammals, the monotremes excepted, no cloaca is form- 
ed. The vent is on the lower surface, in the median 
line. 

There are several accessory structures connected with 
the alimentary canal. Thus frequently salivary glands 
are present, emptying into the mouth. Behind the 
stomach the ducts of the liver and pancreas pour in their 
secretions, while in many fishes well-developed pyloric 
caeca occur, just behind the stomach, which have a diges- 
tive function. 

The digestive organs are supported in the body-cavity 
by a thin membrane {mesentery) which bears blood- 
vessels, etc., and which is attached to the dorsal wall of 
the body-cavity. This mesentery in reality is but the 
continuation of the lining {peritonaeum) of the body- 
cavity. 

Vertebrates respire in three ways: by gills, by lungs, 
and by the skin. Gills arise first as outpushings or pouches 
in the sides of the pharynx, and then these break through 
to the exterior, giving rise to gill-slits or clefts, through 
which water taken in at the mouth can pass out. On the 
sides of these clefts the gills proper are developed. These 
are thin-walled leaves or filaments with a rich blood- 
supply, and through these thin walls there is an exchange 
of dissolved gases (oxygen and carbon dioxide) between 
the water and the blood. 



308 



SYSTEMATIC ZOOLOGY. 



in the septa between the gill-slits are the gill-arches or 
cartilages (p. 294) ; and from the septa there grow out, 
in the larval Amphibia, fleshy fringes, the external gills. 





Fig. 115.— Relations of gills, gill-openings, etc., in a shark (left) and a teleost 

(right). 

In most Amphibia these external gills are later absorbed 
and replaced by internal gills, which in turn may disap- 
pear upon the assumption of an aerial respiration. 

The number of these clefts varies between four and 
eight (more in some cyclostomes) , but in all gnathostomes 
the anterior cleft has largely lost its respiratory function. 
In the sharks it becomes modified into the spiracular 
cleft; in the higher vertebrates it enters into the struc- 
ture of the ear, giving rise to the cavity of the drum and 
to the Eustachian tube (p. 303). 

In the sharks (fig. 115) each cleft opens separately to 
the exterior; but in ganoids and teleosts the hyoid sep- 
tum gives rise to a fold (operculum) or gill-cover, which 
grows back over the external openings, so that there is 



VERTEBRATES. 



309 




Fig. 116. — Humanembryo 
(after Hertwig), with 
the floor of mouth and 
throat removed, to show 
the rudimentary gill- 
slits, g. I, lung; n, nos- 
tril, still connected with 
the mouth. 



apparently but a single slit externally. A little con- 
sideration will show that there is 
little real modification. In the anu- 
rous Amphibia a similar fold is 
found, but this unites again with 
the body-wall behind the gills, thus 
enclosing the external openings in 
an atrium, with but a single open- 
ing to the exterior (p. 337). In the 
Sauropsida and mammals (fig. 116) 
gill-pouches are formed in the em- 
bryo, but according to recent observ- 
ers these never break through, so 
that no real clefts are formed. With 
growth all but the first pair of these 
pouches disappear, the first persisting as the Eustachian 
tube. 

In all vertebrates above fishes, gills are supplemented 
(Amphibia) or replaced by lungs. These are paired sacs 
richly supplied with blood-vessels, and connected with the 
external world by means of a tube (windpipe or trachea) 
which opens by the glottis upon the floor of the pharynx. 
The trachea is usually strengthened by the development 
of cartilages in its wall, some of which may become large, 
as in the case of the human ' Adam's apple.' The lungs 
themselves may be simple sacs, but usually they become 
greatly folded, thus increasing the respiratory surface. In 
the Amphibia, which lack diaphragm and ribs, air is forced 
into the lungs by swallowing; in the reptiles and birds it 
is drawn in by means of the muscles (intercostals) between 
the ribs; in the mammals the intercostals are reinforced 
by a transverse muscle (diaphragm) (fig. 114) which 
crosses the body-cavity. This is dome-shaped, convex 



310 SYSTEMATIC ZOOLOGY. 

above, becoming flatter by contraction and thus enlarging 
the cavity (thoracic cavity) which lies in front of it. 

In the ganoids and bony fishes exists a structure, the 
swim-bladder or air-bladder, which is usually thought to 
represent the lungs. In the lower teleosts (Physostomi) 
it is connected with the alimentary canal by a duct open- 
ing on the dorsal wall of the pharynx, but in others (Physo- 
clisti) this duct closes long before the adult condition is 
reached. In the lung-fishes, on the other hand, the 
structure is double and its duct ventral. 

Connected with the respiratory system are two glands of 
problematical function. One of these, the thyroid, is 
formed from the floor of the pharynx. The other (the 
thymus) arises from the gill-pouches, and in the higher 
vertebrates disappears in adult life. In the calf it forms 
the 'neck sweetbread.' Both these glands are without 
ducts, and the part they play is obscure, but since when 
the thyroid is diseased it produces serious illness, it is 
apparent that it is very important in the economy. 

In the circulatory system three parts may be recognized: 
(1) a central propelling organ, the heart; (2) arteries, 
carrying the blood away from the heart; and (3) veins 
bringing it back. Between arteries and veins are inter- 
posed minute tubes, the capillaries. 

The heart is a muscular organ, enclosed in a special sac 
of the body-cavity, the pericardium. In the heart can 
always be distinguished a receptive portion (auricle), which 
receives the blood as it comes from the veins, and passes 
it on to the true propelling organ, the ventricle. This 
latter has strong muscular walls, and when it contracts, 
the blood, prevented by a valve from returning to the 
auricle, is forced out through the artery (ventral aorta) 
connected with the ventricle. 



VERTEBRATES. 311 

In all fishes there is but a single auricle and a single ven- 
tricle, but when lungs appear, as in the Amphibia, the 
auricle becomes divided, and now one half (the right) 
receives the blood from the body, while the left auricle 
takes the blood returning from the lungs. These both 
pour the blood into the single ventricle. In the reptiles 
we find the beginning of a division of the ventricle, which 
becomes complete in the crocodiles and continues in 
birds and mammals (fig. 118). In these forms the left 
auricle pours its blood into the left ventricle, while the 
same relations exist between the auricle and ventricle of 
the right side. 

In the fishes the blood leaves the ventricle by an arterial 
trunk, in which, when best developed, we can distinguish 
a conus with valves inside to prevent the blood flowing 
back into the ventricle; or a bulbus, without valves, and 
in front of these the ventral aorta. From this lateral ves- 
sels "(afferent branchial arteries) are given off, and these 
pass up through the branchial septa. Consequently the 
number of these arteries depends primarily upon the num- 
ber of gill-clefts. In the septa the arteries break up into 
capillaries which pass through the gills, and collect in 
efferent branchial arteries which pass above the pharynx. 
Here they unite and give rise to the main trunk, the 
dorsal aorta, which runs, above the alimentary canal, 
through the body, giving off vessels to all parts, see fig. 
117, A. 

From these vessels the blood passes through the capil- 
laries and is collected in veins which bring it back to the 
heart to repeat the circuit. In this circulation the blood 
changes in its character. When it enters the heart it 
bears nourishment obtained from the alimentary canal, 
and waste from all parts of the body. Its color is a dark 



312 



SYSTEMATIC ZOOLOGY. 



purplish red. In its passage through the gills it rids itself 
of one kind of waste (carbon dioxide) and absorbs oxygen 
from the water. This exchange is accompanied by a 
A BCD 

c EC 




Fig. 117. — Diagram of the arterial arches and their modifications in various 
vertebrates (after Boas). The primitive arches are outlined; those which 
are functional in the adult are black. A , embryonic condition ; B, Ceratodus 
(fish); C, Salamandra; D, Triton; E, frog; F, lizard; G, bird; H, mammal; 
C, carotid artery; DB, ductus Botallii; DO, dorsal aorta; EC, external carotid; 
IC, internal carotid; P, pulmonary artery ; SC, subclavian artery ; VO, ven- 
tral aorta; 1-6, primitive arches. 

change of color to bright red. The other waste is gotten 
rid of in the kidneys. In the capillaries of the body it 
gives up its oxygen and nourishment to the surrounding 



VER TEBRA TES. 813 

parts, and becomes loaded anew with carbon dioxide and 
other waste, changing color again to the dark red. From 
this account it will be seen that in the fish only blood 
charged with impurities passes through the heart. 

From the arrangement of blood-vessels found in the 
fishes (sharks) all the conditions found in the higher verte- 
brates may be derived, simply by enlarging some vessels 
and suppressing others. Some of the changes involved 
may be made out from the diagrams (fig. 117) in compari- 
son with your dissections, the explanatory statement being 
made that in embryo birds and mammals paired branchial 
arteries occur, while in the adult this symmetry is largely 
lost. One point particularly to be mentioned is that with 
the development of lungs, 'pulmonary arteries going to these 
organs are developed from the hinder pair of branchial 
arteries (fig. 117, B-E, P). 

When the gills are lost and the lungs function as respi- 
ratory organs, the conditions of the circulation are changed. 
The blood, in leaving the heart, passes partly to the various 
parts of the body, partly to the lungs. . That going to the 
latter organ loses its carbon dioxide, and takes up oxygen 
and changes to bright red, It now returns along with 
blood from other parts to the heart, which therefore now 
receives both light and dark blood and forces the same 
out again. But when the lungs are developed the auricle 
of the heart divides, and one auricle receives the dark, the 
other the light blood, both emptying their contents in turn 
(in frogs and reptiles) into the single ventricle. It was 
therefore formerly thought that the blood sent out through 
the ventral aorta must necessarily be mixed; but this is 
not the case with the frog. By means of a peculiar valve 
the red blood is sent to the body, the dark blood to the 
lungs. 



314 



SYSTEMATIC ZOOLOGY. 



As has already been mentioned, in crocodiles, birds, and 
mammals the ventricle is also divided, and hence one half 
of the heart contains only bright , 
the other only dark, blood. The 
division is also car ied farther, for 
the last arch (going to the lungs) 
becomes connected with the half of 
the heart which receives the dark 
b ood, while the rest of the arches 
are similarly related to the other 
half of the heart (fig. 118). 

The blood itself should have a 
moment's attention. It consists of 
a fluid (plasma) in which float myri- 
ads of minute solid bodies (corpus- 
cles). The plasma is a pale yellow 
in color, the red of the blood being 
due to certain of the corpuscles, 
which are therefore known as the 
red corpuscles. Other corpuscles 
are colorless, and are called white 
corpuscles or leucocytes. The red 
corpuscles carry the oxygen and 
carbon dioxide, the plasma the 
nourishment and the other waste. 
The plasma is further peculiar in 
that when withdrawn from the veins it soon solidifies 
or ' clots/ 

The excretory organs (kidneys or nephridia) are very 
complicated structures. In a few words, they may be 
described as a pair of organs lying in the dorsal wall of 
the body-cavity close to the median line. Each kidney 
is richly supplied with blood, and it extracts from this 




Fig. 118.— Diagram of the 
circulation in a mam- 
mal. The arrows show 
the direction of the flow ; 
the vessels carrying red 
blood are shown white, 
those carrying dark 
blood, shaded, a, au- 
ricles;/, lung; Iv, liver; 
p, portal vein bringing 
the blood from the in- 
testine; v, ventricle. 



CYCLOSTOMES. 315 

fluid the nitrogenous waste and pours it into an excretory 
or urinary duct which empties behind, near the anus. 

The reproductive system is closely related to the excre- 
tory organs. In all except a few fishes the sexes are sepa- 
rate. In the females, eggs are formed in special structures, 
the ovaries, and when ripe the eggs are passed out to the 
exterior by means of a tube (oviduct) developed from the 
urinary duct. This passage may be rapid, or the egg may 
remain for a time in the oviduct and there undergo its 
development, as is the case in certain members of all 
groups of vertebrates except birds. 

In the male, corresponding to the ovaries in position, 
etc., are the testes, which produce the male reproductive 
element, which is also carried off by a part of the primitive 
excretory duct. 

All vertebrates produce eggs, but these vary consider- 
ably in size. In the mammals the diameter is about -j-J-jr of 
an inch, the ostrich lays an egg about 5 inches in diam- 
eter, while the egg of Mfiornis, one of the extinct birds of 
Madagascar, was equal in size to 150 hen's eggs. 

The Vertebrates are divided into Cyclos tomes and 
Gnathos tomes. 

Series 1.— CYCLOSTOMATA. 

The Cyclostomes include a few eel-like forms, commonly 
known as lampreys and hagfishes. These differ from the 
other Vertebrates in many points, some of which are 
mentioned here. Bone is entirely lacking, and cartilage 
is feebly developed. Vertebrae are scarcely recognizable, 
and there are no traces of paired fins, although dorsal and 
caudal fins may occur. The mouth, as the name Cyclo- 
stome implies, is circular, but is incapable of closure like 



316 SYSTEMATIC ZOOLOGY. 

that of other vertebrates, since movable jaws are lacking. 
Inside of the mouth are horny teeth (few in the hagfishes, 
many in the lampreys), but these are chiefly used for 
holding, not for biting or crushing. The tongue is very 
large. 

There is but a single nostril on top of the head. The 
gills are placed not in simple slits, but in large pouches on 
the sides of the neck (hence the name, Marsipobranchs, 
often given the group), and these pouches may either 
open separately to the exterior or by means of a tube 
which leads to a single opening. The number of gill- 
pouches ranges between six and fourteen on either side. 

The Cyclostomes are subdivided into two groups, accord- 




Fig. 119. — Lamprey (Petromyzon marinus). After Goode. 

ingly as the nostril communicates with the throat or not. 
As examples of the first, the hagfishes may be cited. 
These are all marine, and are capable of secreting a large 
amount of mucus from their bodies, so that a few hagfish 
in a pail will convert the water into a jelly-like mass. 
These fishes are parasites, and work their way into vari- 
ous fishes, like the cod, and when once inside they eat up 
all the flesh and viscera, leaving nothing except the skin 
and bones. 

The second group is represented by the lampreys. Some 
of these are marine, others live in fresh water, while many 
of the marine forms ascend streams in spring to lay their 



FISHES. 317 

eggs. By means of their circular mouths, horny teeth, 
and sucking tongues, the lampreys attach themselves to 
fishes, from which they suck the mucus and frequently 
the blood. In some places the large sea-lampreys are 
regarded as delicacies, but usually they are not esteemed 
as food. 

Series II.— GNATHOSTOMATA. 

This group, the name of which means jaw-mouth, 
includes the great majority of vertebrates in which true 
jaws, capable of closure, occur. The skeleton, sometimes 
of cartilage, sometimes of bone, is a true support to the 
body; usually paired limbs are present, and there are a 
pair of nostrils. The preceding general account of the 
Vertebrata (pp. 290 to 315) applies especially to the 
gnathostomes. The group is subdivided into Ichthyop- 
sida, Sauropsicla, and Mammalia. 

Grade I.— ICHTHYOPSIDA (Fish-like Forms). 

Under this name are grouped fishes and batrachians, 
since they are alike in certain important respects. Thus 
they have, either as larvae or adults, functional gills, they 
have lateral-line organs, they have median fins, and the 
blood is cold. Besides these there are several other points 
of union, notably in the development, especially promi- 
nent being the absence of two embryonic structures, the 
amnion and allantois, which occur in higher forms. The 
Ichthyopsida are divided into two classes: Pisces and 
Amphibia. 

Class I.— PISCES (Fishes). 

The forms to which the name Fishes is usually applied 
have a body adapted in shape and structure for an aquatic 
life. It is usuahv covered with scales, which lie between 



318 SYSTEMATIC ZOOLOGY. 

the two layers (corium and epide mis) of the skin, the lat- 
ter extending over them. These scales may be of four 
kinds, the placoid, ctenoid, cycloid, and ganoid. Placoid 
scales are hard plates, in structure much like teeth, with 
usually a spine projecting backwards from the surface. 
Cycloid scales are much softer, more or less circular in 
outline, and with no projecting spine. Ctenoid scales differ 
from cycloid in having the free edge of the scale toothed 
somewhat like a comb. Ganoid scales are either rhomboid 
or circular in outline and are covered externally with a 
peculiar enamel layer. At one time fishes were classified 
according to the scales, but this was found to be unnatural. 
The fins are adapted to fanning the water, being broad 
plates with an internal stiffening skeleton. Usually both 
anterior and posterior paired fins are present, and these 
are supported on skeletal girdles (pectoral in front, pelvic 
behind), which extend across the body beneath, but which 
have no connection with the vertebral column, nor with 
any structure like a breast-bone. The pectoral, however, 
is frequently joined to the skull. The paired fins are 
largely organs of balancing and of directing the body 
upwards or downwards ; the caudal is the chief swimming- 
organ. The caudal fin presents three interesting con- 
ditions. In all fishes it is at first diphy cereal (fig. 120, A); 
that is, the vertebral column runs out in a straight line, 
dividing the fin into equal and symmetrical halves. This 
condition is retained in a few forms. In others, with 
growth, the vertebral axis becomes bent upwards, and a 
secondary lower lobe is developed which, as it is smaller 
than the other, gives the heterocercal condition (fig. 120, B). 
This condition is permanent in the Selachii and most 
ganoids, but in the bony fishes the lower lobe grows out 
equal to the other, and the tail becomes homocercal, 



FISHES. 



319 



although the skeleton shows a bent back-bone (fig. 120, 
C,D). 




Fig. 



120. — Different forms of tails of fishes. A, diphycercal; 
cereal; C, D, homocercal. (From Zittel.) 



B, hetero- 



There are two nasal sacs, although frequently four 
nostrils are present, the four arising by a closure of the 
two primitive openings in the middle. Inside the sac is 



320 SYSTEMATIC ZOOLOGY. 

the folded olfactory membrane. In no case is there any 
connection of the nasal cavities with the mouth or throat, 
although it is interesting to note that in the skates a 
groove leads backward from each nostril to the mouth, 
recalling the way in which the internal nostrils are formed 
in the young of the higher vertebrates. 

The gill-slits start/ as paired outpushings from the throat, 
which later break through to the exterior. These may all 
retain their separate external openings, or they may be 
covered up by a fold from the back side of the head grow- 
ing over them and forming an operculum. (See also p. 
308). Water taken in through the mouth is forced out 
through these slits, and is thus brought in close contact 
with the thin- walled gills lining their sides. 

In many forms an air-bladder occurs. This arises as 
an outgrowth from the dorsal wall of the oesophagus or 
gullet, and in many this connection persists throughout 
life (Physostomi), but in others the duct is closed later. 
The bladder serves as a hydrostatic apparatus, and when 
it is expanded the specific gravity of the fish is lessened 
and the animal can rise, while when it is compressed the 
animal sinks. In some forms the bladder is used in pro- 
ducing a noise. 

In all fishes the heart, situated in a pericardial chamber, 
consists of two portions: an auricle, which receives the 
blood returning from the body, and a ventricle, which 
forces it forward through the gills to all parts of the animal. 
In leaving the heart proper the blood first passes through 
an arterial cone or an arterial bulb (fig. 121)-. These 
differ in this: the arterial cone is really an outgrowth of 
the heart, and contains, on its interior, valves to prevent 
the flow of the blood back into the ventricle; the arterial 
bulb, on the other hand, is merely a muscular thickening 



FISHES. 



321 



of the ventral aorta, and contains no valves. After pass- 
ing through the afferent and efferent branchial arteries 
(p. 311) the blood is collected in the dorsal aorta and 
thence distributed to the body. 

The blood, returning to the heart, bears with it the 
waste from all parts of the body, and prominent among 
this is carbonic dioxide; in short, it is what physiologists 




Fig. 121. — Types of Fish-hearts, a, auricle; b, bulbus; c, conus; v, ventricle. 

call venous blood. This is forced forward, through the 
ventral aorta and the branchial arteries, to the gills. 
Through the thin walls of these it comes in close connec- 
tion with the water, and the carbonic dioxide is given off, 
while oxygen, from the air dissolved in water, is taken 
into the blood, which thus becomes arterial blood, and is 
distributed to all parts of the system through the dorsal 
aorta and other vessels. Hence, as will readily be under- 
stood, the heart of the fishes, in contrast to that of all 
other vertebrates, receives only venous blood. 

It is interesting to note why a fish dies when taken from 
the water. It is simply because it cannot obtain air 
enough. When the fish is in the water the gills are floated 
out so that all parts of them are exposed to the stream 



322 SYSTEMATIC ZOOLOGY. 

passing through the gill-slits. When the fish is out these 
delicate filaments mat together, reducing the surface for 
breathing ; and then, too, the gills soon become dry, and 
then are less favorable for the exchange of carbonic 
dioxide and oxygen. 

Among the peculiarities of the skull are the numbers of 
branchial arches and the ease with which these, the oper- 
cular structures, and bones of the face can be separated 
from the cranium (p. 293). In the Selachii these, like 
the rest of the skeleton, are composed of cartilage. In 
the Teleosts this is largely replaced by bone. Another 
peculiarity is that the lower jaw does not directly join 
{articulate with) the skull, but certain parts intervene 
between the two, forming what is known as a suspensory 
apparatus (see p. 294). 

The group of Pisces is divided into four subclasses: 
Elasmobranchii, Ganoidei, Teleostei, and Dipnoi. 

Subclass I. — Elasmobranchii (Selachii, Sharks, and 
Skates). 

These forms, of which the dogfish is an example, are, 
with few exceptions, marine. They are sharply marked 
off from all other fishes by several characters. The 
skeleton is entirely of cartilage, no bones being developed; 
the body is usually covered with placoid scales (p. 318); 
the gill-slits (five to seven in number) open separately to 
the exterior, except in the Holocephali, and no operculum 
is developed; the heart has an arterial cone, and the intes- 
tine is provided with a spiral valve. There is usually a 
spiracle, and the air-bladder is always lacking. The 
mouth and nostrils are usually on the ventral surface. 
The Elasmobranchs are, on the whole, the most primitive 
of the jawed vertebrates and hence they have been studied 



FISHES. 



323 



to a great extent, since no other forms give such a clear 
understanding of the characters of the group. Of the 
several orders, only the Squali, Raise, and Holocephali 
need mention here. 

Order I. — Squali (Sharks). 

In the sharks the body is more or less cylindrical, and 
the gill-slits open upon the sides of the neck. About 150 




Fig. 122. — Sawfish 
(Pristis pectinatus). 
After Goode. 



Fig. 123. — Common Skate (Rata erinacea). 



species are known, some, like the dogfish, being small, 
others reaching an enormous size. Those sp ecies which 



324 SYSTEMATIC ZOOLOGY. 

feed on fish and the like have sharp cutting teeth, and 
these are arranged in rows, one behind another, so that 
only one row is in use at a time, the other serving as a 
reserve supply if one of the front row be lost. In other 
sharks, which feed on shell-fish, the teeth are flattened 
plates, the whole forming a mill for crushing the shells. 
Most of the species are much like the dogfish in their 
general appearance, but there are strange forms. Thus 
in the hammer-head sharks the sides of the front of the 
head are drawn out like a mallet, the eyes being on the 
outer ends of the lobes. In the sawfishes the snout is 
drawn out in a long beak, either edge of which is armed 
with sharp teeth. 

Order II. — Rai^e (Skates, Rays). 

In the skates and rays the body is usually flattened, and 
the gill-slits are on the under surface. In most forms the 
body is sharply marked off from the tail, but in those saw- 
fishes which belong to this order the body is shark-like. 
The width of body in the true skates is partly due to 
the fact that the pectoral fins are enclosed in it, the whole 
making a disk, rounded or four-sided in outline. Most of 
them are bottom feeders, living upon shell-fish, and hence 
have flattened pavement-teeth. The torpedoes are remark- 
able for their electrical powers. In them certain muscles 
on the sides of the head are metamorphosed into an elec- 
trical battery, the discharge of which is under control of 
the will. The current is strong enough to kill small 
animals which come into contact with the creature. . The 
largest of the skates are the huge tropical devil-fish, which 
reach a length of twelve or more feet and a weight of 1200 
pounds. 



FISHES. 



325 



Order III. — Holocephali. 

A group of less than ten species of strange marine car- 
tilaginous fishes in which the upper jaw is firmly united to 
the cranium, the gills are covered by a flap of skin, like 
an operculum, and a spiracle is lacking, compose this order. 




Fig. 124. — Chimcera monstrosa. 



Mouth and nostrils are ventral, as in the sharks. The 
name Chimcera, given to some forms, emphasizes their 
strange appearance. Little is known of their habits. 



Subclass II. — Ganoidei. 

These are remnants of a group once very abundant on 
the world's surface, but now showing less than fifty living 
species in the whole world, and most of these in North 
America. Some of them are much like Selachians, others 
like Teleosts, and still others go off towards the Dipnoi. 
The skeleton is bony or cartilaginous; the body may be 
covered with ganoid or cycloid scales, or with bony plates, 
or it may be naked; the tail either homo- or heterocercal ; 
the gills are covered with an operculum. The heart is 
provided with an arterial cone, and the intestine has a 
spiral valve. A swim-bladder occurs, and this has its 
duct, which, in one form, empties into the ventral side of 
the oesophagus. With this confusing mixture of characters 



326 SYSTEMATIC ZOOLOGY. 

it is not strange that many naturalists have split up the 
group and distributed its members among the other sub- 
classes. 




Fig. 125. — Common Sturgeon (Acipenser sturid). After Goode. 

To it belong the sturgeons (fig. 125), the most sharklike 
of all, some of which live in fresh water, while the marine 
forms ascend the rivers to lay their eggs. From their 
ovaries are made caviare, while their swim-bladders fur- 
nish the isinglass, now so largely supplanted in domestic 
economy by gelatine. Though some attain an enormous 
size, all feed upon small animals, worms, insect larvae, etc., 
which they find in the mud. The garpikes (fig. 126), 




Fig. 126. — Garpike (Lepidosteus osseus). After Tenney. 

with their strongly armored bodies, which also belong 
here, on the other hand, are very voracious. The bowfin 
of the United States is the most like Teleosts of all the 
ganoids. 

Subclass III. — Teleostei (Bony Fishes). 

The great majority of the forms which we ordinarily call 
fishes belong to the group of Teleosts or bony fishes, so 
called from the abundant bony matter in the skeleton. In 
all, the mouth is at the tip of the snout, the nostrils on the 



FISHES. 327 

upper surface, and the caudal fin, though heterocercal in 
the young, is homocercal in the adult.* The skull is cov- 
ered with numerous bony plates, and the body is covered 
with either cycloid or ctenoid scales. Sometimes (trout) 
scales are apparently lacking, but this apparent absence 
may be due to their small size and their being buried in the 
skin. The gills are covered by an operculum. Of the 
internal features which characterize the group may be 
mentioned the absence of a spiral valve in the intestine, 
the presence of an arterial bulb in the heart, and, very 
frequently, of a swim-bladder. 

The ten thousand species of bony fishes are variously 
subdivided by naturalists accordingly as different structures 
are made the basis of classification. One of the simplest 
of these schemes recognizes six subdivisions or orders, 
and is adopted here. To which does the specimen you 
studied belong? 

Order I. — Physostomi. 

Bony fishes in which the gill-filaments are arranged on 
the branchial arches like the teeth of a comb; with the 
premaxillary and maxillary bones movable (p. 24) ; the 
dorsal, anal, and ventral fins supported only by soft rays 
(p. 23); the ventral fins, when present, placed near the 
vent. An air-bladder is almost always present and 
retains its connection with the throat throughout life 
(p. 310). The scales are usually cycloid (p. 318). Most 
of the species belong in fresh water. 

The catfishes and horned pout, with long filaments or 
barbels about the mouth, belong here. In our eastern 
waters the species are small, but in the Mississippi basin 

* In a very few the tail remains diphycercal throughout life. 



328 SYSTEMATIC ZOOLOGY. 

large species occur , some weighing 100 pounds or more. 
Many more species occur in the tropics of Africa and 
America, and some of these have the scales greatly devel- 
oped so that they form a bony armor. One African 
species, like the electrical eel and the torpedo, can give a 
sharp electrical shock. 

The carp and minnows abound in fresh water, but, 
excepting as they furnish food for other fishes, they are 
of little importance; the carp of Europe having a slight 
value as food for man. The goldfishes of Chinese origin 
also belong here. 

Much more valuable is the group of trout and salmon, 
which are among the most important of food-fishes. As a 
rule these have a soft fin behind the rayed dorsal. The 
salmon, of which there are one species on the Atlantic 




Fig. 127. — Atlantic salmon (Salmo salar). After Goode. 

(fig. 127) and four on the Pacific coast, live in the sea 
and enter the rivers to lay their eggs. The whitefish of 
the lakes are closely allied forms. 

The blindfish of Mammoth Cave should be mentioned 
here. In this form a. life in total darkness has resulted in 
the degeneration of the eyes, which are buried -beneath the 
skin. 

The savage, swift-swimming pike, pickerel, and muska- 
longe, the latter reaching a length of eight feet, are, with 
one exception, confined to America. They are noted for 



FISHES. 329 

their voracity, and have been termed "mere machines for 
the assimilation of other organisms." 

Among the marine members of the order are the her- 
ring (fig. 128), shad, menhaden, fishes of great importance 
to man, both as food and for the oil and fertilizers which 




Fig. 128. — Herring (Clupea harengus). 

are made from them. They occur in large schools, and 
afford food for numerous predaceous fishes. 

Differing from the forms already mentioned are those 
which may be grouped together as eels, fishes with elongate 
bodies and without ventral fins. Most of the species are 
marine, and those which live in fresh water go to the sea 
to spawn. All are voracious creatures, and one South 
American species has marked electrical powers. 

Order II. — Anacanthini. 

These have the gills comb-like (p. 327) ; the dorsal, anal, 
and ventral fins without spines; the ventral fins, when 
present, placed far forward between the pectorals; the 
swim-bladder without connection with the gullet; and the 
scales either ctenoid or cycloid. Mostly marine. 

But few of these forms need mention. Most important 
of all are the cod (fig. 129) and haddock, which stand 
beyond all others as food-fishes. They occur in the north- 



330 



SYSTEMATIC ZOOLOGY. 



ern parts of both oceans, and find their favorite feeding- 
grounds on those shallow spots known as ' banks.' The 
Grand Banks of Newfoundland are constantly visited by 
fishermen from Europe and America, and have aptly been 




Fig. 129. — Cod (Gadus morrhua). After Storer. 

said to be the richest banks in the world, honoring every 
draft upon them. 

Allied to the cod is the strange group of flatfishes, the 
halibut, flounders (fig. 130), turbot, and the like. In 




Fig. 130. — Winter Flounder (Pseudopleuronectes americanus). After Goode. 

early life these are symmetrical like other fishes, but as 
they grow older they turn over on one side, and then the 



FISHES. 331 

eye of that side migrates to the upper surface, twisting the 
bones of the skull in its progress. Henceforth the fish 
lives constantly in this peculiar position, the side of the 
body turned downward being white, the other colored. 
The halibut, occurring in all northern seas, are among 
the largest fishes, occasionally weighing 350 to 400 pounds. 

Order III. — Acanthopteri (Spiny-finned Fishes). 

In this, the largest order of bony fishes, the gills are 
comb-like, the jaw-bones are movable (p. 24), and the 
dorsal, anal, and ventral fins have spiny rays in front. In 
some there is a swim-bladder, but it is without connection 
with the gullet. Among the strange modifications in the 
group are the suck-fish or Remoras (fig. 131), in which 




Fig. 131. — Rem or a (Remoropsis brachyptera). After Goode. The sucker is 
shown on the top of the head. 

part of the dorsal fin is modified into a sucker, by which 
they attach themselves to other fishes or floating objects, 
and are thus carried about. 

In the swordfishes the bones of the upper jaw are modi- 
fied into a long, stiff sword terminating the snout, and 
used as a weapon of offence and defence. The largest 
species reaches a length of fifteen feet. In other points 
of structure the swordfish are much like the mackerels, 
(fig. 132), pompanos, and bluefish, so well known as food- 
fish. Of these the largest is the tunny or horse-mack- 
erel, which sometimes weighs 1500 pounds. 



332 SYSTEMATIC ZOOLOGY. 

In another group of perch-like forms the spines of the 
fins are more developed. Here belong the perch, sea- 
bass, and porgies ; the sheepshead and fresh-water sunfish, 
the sculpins, and a long series too numerous to mention. 




Fig. 132. — Mackerel (Scomber scombriis*). 

Order IV. — Pharyngognathi. 

These are Acanthopteri in which the last branchial 
arches are fused into a single bone, which thus resembles 
an additional jaw in the throat, whence the name (pharynx- 




Fig. 133. — Cunner (Ctenolabrus coeruleus). After Goode. 

jaw). All of the species are marine, and with few excep- 
tions they are tropical. On our east coast are found the 
cunner (fig. 133) and tautog; on the Pacific occurs a 
group of surf -fishes (Embiotocidae), remarkable for bring- 
ing forth living young. 



FISHES. 333 

Order V. — Plectognathi. 

In this group of peculiar forms, almost all of which are 
marine, the upper jaws are immovably united to the skull. 
Some are naked, others have the skin covered with spines 
or bony plates. The spiny forms (swellfish— fig. 134) can 




Fig. 134. — Swellfish (Chilomycterus geometricus). After Goode. 

erect the spines by swelling out the body, and thus gain 
additional protection. In the trunkfishes the bony plates 
unite to form a solid box. In the sunfishes of the ocean 
(fig. 135), which may weigh 1800 pounds, the body is 
almost circular in outline, and has a distinctly chopped- 
off appearance. As a whole, the order bears most re- 
semblance to the Acanthopteri. None are of the slightest 
economic importance. 

Order VI. — Lophobranchii. 

These are the most aberrant of bony fishes. The gills, 
as the name implies, are tufted, and composed of small 
rounded lobes packed in the gill-chamber. The oper- 
cular apparatus is reduced to a simple plate, the small, 
toothless mouth is at the end of a long snout, the skin is 
covered with bony plates arranged in rings around the 



334 



SYSTEMATIC ZOOLOGY. 



body. The species, which are all small, are known, from 
their fanciful shapes, as pipefishes and sea-horses (fig. 136). 




Fig. 135. — Sunfish {Mola rotunda). After Putnam. 

Many have a remarkable peculiarity in breeding habits, in 
that the young are carried for a time in a pouch beneath 
the tail of the male. 

Subclass IV. — Dipnoi (Lung-fishes). 

Four species, one from Australia, one from Africa, and 
two from South America, are the sole living representa- 



FISHES. 335 

tives of this group, which, however, occurs as fossils in 
very old rocks. They have scaly bodies, diphycercal tail, 




Fig. 136. — Sea-horse (Hippocampus heptagonus). After Goode. 




Fig. 137. — African lung-fish (Protopterus annectens). After Boas. 

spiral valve, and a swim-bladder which is used as a lung. 
Both pectoral and ventral fins are present, and these are 



336 SYSTEMATIC ZOOLOGY. 

supported by a peculiar skeleton, while the skull shows 
many strange features. The lung-fishes present many 
points of interest for the naturalist. By many they are 
supposed to be nearest to the line from which the Amphibia 
have sprung. 

Class II.— AMPHIBIA (Batrachia). 

The frog may serve as a type of the Amphibia, which, 
so far as living representatives are concerned, are marked 
off from the fishes by a number of important characters. 
With very few exceptions the Amphibia pass at least a 
part of their life in the water, and many, in reaching the 
adult condition, pass through great changes in structure 
(all are familiar with the metamorphosis of the tadpole 
into the frog), so that, in considering the group, the char- 
acters of both larva and adult must be taken into account. 

In all the skin is very glandular and in all, except the 
tropical group of blindworms, scales are lacking, and, ex- 
cepting again these same limbless forms, fins have given 
place to legs, much like the limbs of man, and like them 
ending typically with five digits. In the larva? of all there 
is a tail, and some (salamanders and newts) retain this 
structure during life, while in others, as in the frog, 
it is absorbed (not dropped off) during growth. The lar- 
val tail bears a median fin, but this is never divided into 
dorsal, caudal, and anal, and it differs further from the 
fins of fishes in having no internal skeleton. 

Of internal features those most distinctive are the 
skeleton of the limbs, unlike that occurring in any fish; 
the union of the pelvic girdle with the back-bone; the 
existence of an Eustachian tube in connection with the 
ear; the connection of the nostrils with the cavity of 
the mouth; and the presence of two auricles in the heart. 



AMPHIBIANS. 



337 



In the larvae respiration takes place by gills, recalling 
those of fishes ; and in a few forms these are retained during 
life. Besides gills, all, in the adult condition, develop 
lungs,* which grow out from the pharynx, and always re- 
tain their connection with it by means of a windpipe (tra- 
chea) opening upon its floor (compare p. 310). The gills 
are fewer in number than in any fish, and only three or 
four gill-slits are formed. Between these slits are devel- 
oped external gills (fig. 138). Later the slits are closed 




Fig. 138. — Larval stage of a salamander with external gills. From Hertwig. 

in those salamanders which lose the gills, by the growing 
together of the slits. In the frogs the process is preceded 
by the formation of an opercular fold (compare fishe?) in 




Fig. 139. — Side view of tadpole. e, eye; g, gill-opening; 
mouth; n, nostril; v, vent. 



I, hind leg; m, 



front of the gill region on either side. These folds grow 
back over the gill-slits, those of the two sides fusing below 
the throat and uniting with the wall of the body above 

* It has recently been shown that some of the North American 
salamanders never develop lungs, but respire solely through the 
skin. 



338 SYSTEMATIC ZOOLOGY. 

and behind the gills, thus forming a large chamber outside 
the gills which is connected with the exterior by a small 
opening on the left side,* through which the water used 
in breathing passes. 

In the larva the heart is two-chambered, and the blood, 
passing forward from it, traverses afferent and efferent 
branchial arteries, as in fishes, and is collected, as in those 
forms, in a dorsal aorta. With the loss of gills and the 
development of lungs the gill circulation changes. The 
first arterial arch becomes converted into the carotid 
artery, supplying the head; the second, the aortic arch, 
connects the heart with the dorsal aorta; the third 
dwindles and usually disappears; while the fourth, the 
pulmonary artery, carries blood to the lungs and skin. 
As will be seen, the embryonic circulation is like that of 
the fishes, but the different condition in the adult is 
brought about not so much by new formations as by 
modifications of pre-existing structures. Compare in this 
connection the diagrams on page 312. 

In the larva the heart pumps only venous blood, as in 
the fish. With the development of lungs and the division 
of the single auricle into two, different conditions occur. 
Blood from the body (venous) is poured into the right 
auricle, and blood from the lungs (arterial, because in the 
lungs it comes into contact with the air) into the left. 
From the auricles the blood goes to the single ventricle, 
and thence through the arterial trunk to head, body, and 
lungs. So at first sight it would "appear as if all parts 
must receive a mixture of arterial and venous blood, but 
this is not exactly the case. By means which cannot 
be described here the purest arterial blood goes to the 

* Right and left openings occur in two tropical toads (Aglossa). 
A few forms have a median opening. 



AMPHIBIANS. 339 

head, the next to the aorta, while the venous blood is sent 
to the lungs. 

In the larvae of the frogs and toads the mouth is small 
and the horny jaws are adapted to scraping small plants 
from submerged objects. Correlated with this vegetable 
food is an extreme length of intestine, it being a notice- 
able fact that herbivorous animals require a longer diges- 
tive tract than carnivorous forms. 

In the larvae there is also a well-developed lateral-line 
system (p. 300), and this persists to some extent in the 
adult of the aquatic salamanders, though disappearing in all 
other forms. 

The vertebral column varies greatly in length, and in all 
except the footless forms it can be divided into neck (cer- 
vical), breast (thoracic), sacral, and caudal or tail regions, 
the sacral being that which connects with the pelvic 
girdle. In some the bodies of the vertebrae are amphicce- 
lous (p. 292) ; in most salamanders they are opisthoccelous 
(rounded in front, hollow behind), while in the frogs and 
toads they are proccelous (hollow in front). The trans- 
verse processes of the vertebra? are different from anything 
in fishes in that they arise from the neural arch and not 
from the centrum. In some forms the ends of these 
processes are jointed, and from this and other facts they 
must be regarded as in part equivalent to ribs. It is to be 
noticed that these ribs never reach the sternum (p. 293), 
which, by the way, is a structure lacking in all fishes. 

A noticeable feature in the Amphibia is the metamor- 
phosis during growth, the chief features of which have 
already been mentioned (p. 337), the result being that 
the adult differs very considerably from the young. 

All living Amphibia live either in fresh water or on the 
land; none occur in salt water. The existing forms are 



340 SYSTEMATIC ZOOLOGY. 

comparatively small, the largest being the giant sala- 
mander of Japan, which may be three to four feet in 
length. Existing Amphibia are conveniently divided into 
three groups or orders: Csecilia, Urodela, and Anura. 

Order I. — Cecilia (Blindworms). 

These are legless, worm-like Amphibia found in the 
tropics of both hemispheres. They have a rudimentary 
tail, degenerate eyes, and the larvae, so far as known, have 
three pairs of gills. Some species form an exception to all 
living Amphibia in having scales in the skin. While highly 
modified in some respects, in others they are the lowest in 
position. They live a burrowing life, feeding upon earth- 
worms, insects, etc., found in the soil. 

Order II. — Urodela (Salamanders, Newts, etc.). 

These forms retain the tail throughout life, and have the 
extremities weakly developed, fitted for creeping rather 
than jumping. Some live in the water throughout life, 
while others, as adults, are to be sought in moist places. 



Fig. 140. — Salamander (Plethodori). 



In some forms the external gills are retained permanently. 
The order belongs almost exclusively to the northern 
hemisphere, and is especially well developed in America. 
Allied to the Urodelans and Caecilians are some enormous 



AMPHIBIANS. 341 

fossils, grouped under the name Stegocephali, some of 
which had skulls five feet or more in length. 

Order III. — Anura (Frogs and Toads). 

These, in the adult condition lack a tail, and have appen- 
dages fitted for leaping. The lower jaw is without teeth. 
The larvse are always tailed, and have at first external 
gills. Frogs (Ranidse) and toads (Bufonidse) differ in that 
frogs have a smooth skin, and teeth in the upper jaw; 
toads have a warty skin (caused by numerous glands) and 
no teeth. Tree-toads (Hylidse) are more frog-like, but 
they have sucking discs on the ends of the toes, by means 
of which they are adapted to a life in trees. Another 
group (Aglossa) occurs in the tropics, in which the tongue 
is absent. 

Some of the Anura have strange breeding habits. Thus 
in the European Alytes the male wraps the long string of 
eggs about his body and carries them there until they 
hatch. In Nototrema of South America the skin of the 
back forms a pouch, in which the eggs are carried; while 
in the Surinam toad (Pipa) the skin of the back becomes 
very much thickened, leaving little cups, in each of which 
an egg is placed, and here the young are hatched out. 

Another interesting form is the flying tree-toad of the 
East Indies, in which the feet with the web between the 
toes become greatly enlarged, forming large discs, upon 
which the animal sails, much as does a flying squirrel upon 
its lateral folds of skin. 



342 SYSTEMATIC ZOOLOGY. 



Grade II.— SAUROPSIDA. 

Although we naturally associate the birds with the 
warm-blooded, hair-bearing mammals, they are structur- 
ally far nearer the reptiles; hence the group which con- 
tains the reptiles and birds is called Sauropsida, which 
means lizard-like. The Sauropsida are distinguished from 
the Ichthyopsida (p. 317) by the fact that at no stage of 
development are functional gills present, and there is 
never a metamorphosis. Scales, which are always present, 
lie not between the two layers of the skin (see p. 318) but 
are composed of the outer layer. The eggs are always 
very large and in their development two structures, the 
amnion and allantois, always occur. The sternum, when 
present, is always connected with the ribs. From the 
mammals they are marked off by the absence of hair, the 
position of the quadrate as the suspensor of the lower 
jaw (p. 294), the articulation of the skull to the vertebral 
column by a single condyle, by the large eggs, and by the 
existence of a cloaca, a common tube into which the di- 
gestive, excretory, and reproductive organs empty. There 
are two classes of Sauropsida, Reptilia and Aves. 

Class I.— REPTILIA (Reptiles). 

The living reptiles closely simulate the Batrachia, and 
in fact the frogs, toads, and salamanders are reptiles in 
popular parlance. The short-bodied turtles are paralleled 
by the frogs, the lizards by the salamanders, and the 
snakes by the blindworms. Yet the differences between 
the two groups are many and important. 



REPTILES. 



343 



The body is more or less completely covered with scales, 
and the toes, when present, bear 
claws. The scales differ from 
those of fishes in being outside 
of the outer layer of the skin. 
These scales differ much in ar- 
rangement, etc. The large plates 
covering the carapace of the tur- 
tle are but enlarged scales, while 
the bony armor of the alligator is 
composed of scales, rendered more 
protective by the development of 
bone in the deeper layer of the 
skin. In the snakes the scaly 
covering is periodically shed. 

By the greater development of 
the neck the heart is carried back 
to a greater distance from the 
head than in the Batrachia. In 
all except the alligators the heart 
is three-chambered, and in these 
the ventricle is incompletely di- 
vided into two. There are two 
aortic arches (fig. 141), but the 
left one, which also supplies the 
stomach, is smaller where it joins 
its fellow to form the dorsal aorta. The blood is 'cold/ 
or rather it is variable in temperature, varying with that 
of the air or water in which the animal lives. 

The brain is small, no part being extremely developed, 
and the optic lobes touch, or may touch, each other in the 
median line. In snakes, lizards, and turtles the cerebel- 
lum is small; in the alligators it is larger. 




Fig. 141. — Arterial Circulation 
of Turtle. a, right aortic 
arch; b, bronchus; /, artery 
to fore limb; h, artery to 
hind limb; p, pulmonary 
artery; r, renal arteries; 
s, arteries to stomach; t, 
trachea; 1, 2, 4, persisting 
aortic arches. Compare 
with fig. 117, E. 



344 



SYSTEMATIC ZOOLOGY. 



The vertebrae are usually proccelous, and the vertebral 
column is divisible- into the regions of neck (ribless), 
thorax (with ribs), lumbar (ribless), sacrum (usually two 
vertebrae which connect with the pelvis), and tail; but in 
snakes these distinctions fail, and only trunk and tail ver- 
tebrae are recognizable. A breast-bone is present in 




Fig. 142. 



-Brain of Snake, c, cerebrum; cl, cerebellum; o, optic lobes; I, 
olfactory nerve; II, optic nerve. 



lizards and alligators, but none occurs in turtles or snakes. 
The skull articulates with the vertebral centrum by a single 
surface (condyle). The hinder angle of the lower jaw is 
connected with the skull by the quadrate bone, which may 
be free (fig. 143), or firmly united to the skull; and the 




Fig. 143. — Skull of Garter-snake (Eutoenia sirtalis), showing the attachment 
of the lower jaw to the skull by means of the quadrate bone, q. (Slightly 
enlarged. ) 



premaxillary and maxillary bones are firmly united to the 
rest of the skull. Teeth are usually present, and in the 
alligators these are inserted in sockets. The shoulder- 
girdle (lacking in snakes) is much like that of frogs, the 
clavicle, however, being absent in alligators. The pelvis 



REPTILES. 345 

is lacking in most snakes, being represented by two bones 
in the boas. The feet, when present, are usually of the 
normal type, the bones of the forearm (ulna and radius) 
and of the shank (tibia and fibula) being separate, and 
the toes, five in number, provided with claws. 

In the embryo, gill-slits are partially developed, but no 
functional gills occur. The lungs are well developed; the 
left one being reduced or absent in the snakes and snake- 
like lizards. Respiration is effected by means of the ribs, 
except in the turtles, and there by a special muscle. 

Both ovaries are developed. The eggs are large, and, in 
those reptiles which lay eggs, are covered with a limy shell. 
A few snakes and lizards bring forth living young. 

Reptiles are most abundant in the tropics, and are lacking 
in cold regions. They are mostly flesh-eaters, some living 
on insects, others on larger forms. Some live on land, 
some in fresh water, and some in the sea. All living 
forms can be arranged in four orders, Lacertilia, Ophidia, 
Testudinata, and Crococlilia. 

Order I. — Lacertilia (Lizards). 

In these the quadrate bone is movable, but the under 
jaw cannot be displaced (c/. Snakes). Legs are usually 
present, but either or both pairs may disappear. When 
the legs are absent the body is exceedingly snake-like, 
but these forms, like all other lizards, may be distin- 
guished at once from the true snakes by the presence of 
small scales on the belly. Only one lizard, the 'Gila 
monster 7 of Arizona, has the reputation of being poison- 
ous, but in former times many, like the basilisk, were 
fabled to have most deadly powers. Among the more 
interesting forms are the 'glass snakes/ go called from 



346 SYSTEMATIC ZOOLOGY 

the ease with which the tail breaks; the 'horned toads/ 
which are not toads ; but true lizards; and the chameleons, 
with their wonderful powers of color change, a capacity 




Fig. 144. — Green Lizard (Anolis). From Lutken. 

which is shared to a less degree by other forms. Among 
others by the Anoles (fig. 144) which are abundant in the 
southern states. 



REPTILES. 



347 



Order II. — Ophidia (Snakes). 

These are like the lizards in the movable quadrate, but 
they differ in the absence of limbs and of sternum, the 
presence of broad scales (scutellre) on the belly, and in the 
fact that the lower jaw is connected with the cranium by 
elastic ligaments, so that it can be displaced in swallowing 
food. Many snakes are poisonous, the poison being con- 




FlG. 145. — Dissection of head of Rattlesnake. /, poison-fangs; p, poison-sac. 



veyed into the wound by specialized teeth, the so-called 
poison-fangs, which are either grooi^ed or are tubular, the 
grooved teeth being capable of being folded back when not 
in use, the others being permanently erect. The rattle- 
snakes (fig. 145) and moccasins belong to the former 
group. The largest snakes, the pythons of India and 
Africa and the boas and anacondas of South America, 
kill their prey by crushing, as do most of the smaller 
snakes — our black-snakes, for example. 

Some snakes are protected against their enemies by 
their colors, which render them inconspicuous in their 
usual haunts; others by the nauseous smell which is pro- 



348 SYSTEMATIC ZOOLOGY. 

duced by certain glands in the skin* still others by their 
poison-glands. Most of the snakes are terrestrial, but 
some, like our water-snakes, take to the water, while in 
the Indian Ocean are found truly aquatic snakes, which 
never go on land and which bring forth living young. 
These sea-snakes are very poisonous. The rattlesnakes 
are the best known poisonous forms in the United States. 
In these the rattle is formed by bits of dry skin, which 
are not lost at the time when the snake sheds the rest of 
its covering. In this way a new joint is added to the 
rattle at each molt, and so the whole becomes an approxi- 
mate index of age. 



Order III. — Testudinata (Turtles). 

The turtles and tortoises are characterized by their 
short bodies, enclosed in a bony shell or box; by the 
absence of teeth; and by the union of the quadrate bone 
with the cranium. The shell, with its two parts, a dorsal 
carapace and a ventral plastron, is composed of an outer 
layer of horny plates (modified scales) and a deeper bony 
layer with which ribs and vertebrae are more or less com- 
pletely united. Into this protective case the head, tail, 
and legs may usually be retracted, and in the box-tortoises 
a hinge in the plastron allows the closure of the openings. 

Some turtles are vegetarians, others are carnivorous. 
Some live on land some in fresh water and some in the 
sea. The largest of existing species are the giant land- 
tortoises of the Galapagos Islands and Mozambique, and 
the leather-back and the loggerhead turtles of tropical 
seas. 

Tortoise-shell, before the days of celluloid, was furnished 
by the dorsal plates of the large tortoise-shell turtle of 



REPTILES. 349 

tropical seas. These plates have the peculiarity that 
they can be united by heat, so that pieces of any desired 
size may be obtained. While many turtles are most 
inoffensive creatures, others, like our snapping-turtles and 
our soft-shell turtles, are ferocious, the young snapper 
showing its temper as soon as it is hatched f re m the egg. 

Order IV. — Crocodilia (Crocodiles and Alligators). 

These forms have the highest development of brain and 
heart of any of the reptiles, the heart being incompletely 
four-chambered. In general shape they are closely like 
the lizards, but in bony and other structural features they 
are greatly different, among these being the immovable 
quadrate. Crocodiles and alligators are distinguished from 
each other by the fact that the former have fully webbed 
feet and more slender snouts. The gavials of the rivers 




Fig. 146. — Restoration of Ichthyosaur (modified from Fraas). 

of India have the snout even more slender. The alli- 
gators are*confined to the New World, while the crocodiles 
occur in both hemispheres. 

The fossil reptiles show a greater range of forms than 
the living species. The Ichthyosaurs represented the 
whales among the reptiles of former times, while the Plesio- 
saurs, also swimming forms, had extremely long necks. 
The Dinosaurs were like the birds in many structural 
features, although they lacked powers of flight and were 
terrestrial or aquatic. Some were enormous in size, hav- 



350 SYSTEMATIC ZOOLOGY. 

ing thigh-bones nine feet in length and vertebrae five feet 
across. The Pterodactyls were flying reptiles with wings 
like those of the bats, except that. the wing-membrane was 
supported by a single finger. 

Class II.— AVES (Birds). 

No one can have the slightest question as to whether a 
certain animal is a bird or not. The feathers, the fore- 
limbs fitted for flight, and the horny, toothless beak are 
characteristic of all living forms. 

Feathers arise from the outer layer or epidermis of the 
skin, and each has its tip inserted in a pit or follicle in the 
integument. Feathers vary considerably. Most promi- 
nent are the large, strongly built contour feathers, which give 
the animal its general shape. Beneath these are the down 
and the pin-feathers. Feathers are not uniformly dis- 
tributed over the body, but are gathered in feather tracts, 
the arrangement of which varies in different birds. The 
feathers are not permanent structures, but they are molted 
or shed and replaced by a new growth, this taking place 
usually once a year. In connection with the feathers 
should be mentioned the oil-glands (the only glands in the 
skin of birds) upon the tail, the secretion of which is used 
in preening the feathers. 

In their origin feathers are much like the scales found 
on the feet, and are probably modifications of such struc- 
tures. The scales on the feet may be small or broad, both 
kinds sometimes occurring on the same foot. The spur of 
the cock is but an extremely developed scale with a bony 
core. These scales, like those of reptiles, differ from those 
of fishes in that they are developed on the outside of the 
outer layer of the skin (compare p. 318). The toes are 



BIRDS. 



351 



terminated by claws; short in the terrestrial; longer in 
the arboreal, forms. Claws occur in some cases, espe- 
cially in young birds, upon the 
wings. 

In all living birds teeth are ab- 
sent, and even in the embryos but 
the slightest trace of their former 
existence can be found. In certain 
fossil birds well-developed teeth oc- 
cur (fig. 150). The tongue is usu- 
ally slender, stiff, and horny, and 
in some forms (woodpeckers, etc.) 
it is very extensible. The oesophagus 
is long, and frequently a part of it 
in the neck is swollen out to form 
a reservoir of food, or crop. The 
stomach is divided into two parts. 
The first of these (proventriculus) , 
which is glandular, appears much 
like an enlargement of the gullet. 
The second or muscular stomach 
(gizzard) is a veritable chewing organ. 
It is most developed in the grain or 
seed-eating birds, and in these often 
contains small stones to assist in 
grinding the food. 

The lungs are especially well de- 
veloped, and a peculiarity is that 
connected with them are air-sacs 

which extend among the other viscera and even into some 
of the bones, as those of the wing.* These air-sacs serve 

* A similar pneumaticity occurred in the bones of some of the 
fossil reptiles (Dinosaurs, p. 349). 




Fig. 147. — A limentary 
tract of an eagle, c, 
crop ; m, muscular stom- 
ach (gizzard); i, intes- 
tine; p, glandular stom- 
ach (proventriculus); t, 
trachea; v, vent. 



352 SYSTEMATIC ZOOLOGY. 

to increase the respiratory surface, and also to lessen the 
specific gravity of the bird. They are also possibly of use 
in changing the position of the centre of gravity during 
flight. 

The heart has four chambers, the single ventricle of 
lower forms being divided into right and left ventricles. 
The large blood-vessels which lead from the heart are, in 
the embryo, much like those of the fish; but with develop- 
ment some parts are altered and others suppressed (fig. 
117, D), so that the result is more modified than in the forms 
already discussed. Thus the left half of the third arch, 
except for an artery (subclavian) going to the wing of that 
side, has entirely disappeared, while the right half, here 
called the arch of the aorta, connects the left ventricle with 
the dorsal aorta. From this the first and third arches, 
modified into carotids, seem to arise. The second arch 
is completely suppressed, while the sixth arch, arising 
from the right ventricle, carries the blood to the lungs and 
forms the pulmonary artery. In returning from the 
body the venous blood is emptied into the right auricle 
and passes thence, through the right ventricle, to the lungs 
for aeration; while that from the lungs goes to the other 
side of the heart, and thence to all parts of the body. 
Hence there is here no mixing of arterial and venous 
blood in the heart. 

In the reproductive organs a constant feature is the 
suppression of the right ovary, a rudiment of it existing 
in a few forms. In the breeding-season the oviduct is 
very large, and from its walls are secreted the white and 
the shell of the egg. The eggs are large, and are always 
enclosed in a limy shell. There is quite a difference in the 
condition in which the young hatch from the egg. Some 
are nearly naked and very helpless (altrices), while others 



BIRDS. 



353 



are thickly clothed with down and are able to run and to 
feed themselves (prcecoces) . 

The brain is large, and, in comparison with the lower 
forms already studied, is noticeable for the great develop- 
ment of the cerebrum and cerebel- 
lum, which by their growth have 
forced the optic lobes apart and 
have covered over the 'twixt-brain. 
The eye is peculiar in that it de- 
parts widely from the spherical 
form, being obtusely conical in front, 
and in that a circle of bones is usu- 
ally-developed in this conical por- 
tion. There is a tube (external 
meatus) developed leading from the 
side of the head in to the ear, and 
this is surrounded by a ring of regu- 
larly arranged feathers. Fig. 148— Brain of Bird. 

In the skeleton, division into neck, thoracic, sacral, and 
caudal vertebrae occurs. The number of neck vertebrae 
varies from eight to twenty-four. The sacrals are notice- 
able for their number, and really embrace, besides the true 
sacrals, some of the lumbars and caudals, which become 
united with the pelvis. The anterior caudal vertebrse 
are free, but the last six or eight are coalesced into the 
pygostyle or plowshare bone. The bodies of the vertebrae in 
living birds are saddle-shaped, that is, concave vertically, 
convex transversely behind, the conditions being reversed on 
the anterior faces. The cervical vertebrae bear short ribs, 
free in the young but firmly united in the adult. Each of 
the true ribs has a small plate (uncinate process) on the 
posterior margin, which connects it with the rib behind 
The breast-bone (sternum) is large and broad, and in 




354 SYSTEMATIC ZOOLOGY. 

flying birds possesses a strong ridge or keel (carina) below, 
to which the muscles of flight are attached. In some 
flightless birds the keel is lacking. 

The skull is noticeable from the great extent of the 
fusion of the separate bones; for the single condyle for 
articulation with the neck and for the suspension of the 
lower jaw by means of a movable quadrate bone, as in 
the lizards, snakes, etc. 

The shoulder-girdle consists of scapula, coracoid, and 
clavicles, the latter noticeable for their union into a V- 
shaped 'wish-bone' or furcula. In the wing the reduction 
in bones of the wrist and hand is remarkable. The bones 
of the wrist are all united into two, while the three fingers 




Fig. 149. — Skull of quail, q, quadrate bone. 

which remain have few joints and are partly united. In 
the hind limb the fibula is short, but especially noticeable 
is the great lengthening of two of the ankle-bones, the 
result being that the heel is elevated some distance from 
the ground. 

Birds are grouped in three divisions or subclasses, 
Saururae, Odontornithes, and Ornithurse, the first two of 
which are extinct; the third contains the ten thousand 
known species of living forms. 



BIRDS 



355 



Subclass I. — Sauruile (Tailed Birds). 

These forms, found fossil in the lithographic stone of 
Bavaria, had tails of extreme length, the feathers being 
arranged on either side of the long tail vertebrae ; and they 




Fig. 150. — Skeleton of wingless tootheJ. bird (ilesperornis). From Marsh. 

had teeth in the jaws. Only two specimens are known, 
the smaller being about the size of a crow, the other some- 
what larger. They are called Archceopteryx. 



356 SYSTEMATIC ZOOLOGY. 



Subclass II. — Odontornithes (Toothed Birds). 

These forms, which have been found only in American 
rocks, are more like modern birds than is Archceopteryx, 
but they differ from all existing birds in having teeth. 
They had normal tails, and one form (Hesperornis, fig. 
150) apparently was wingless, only a rudimentary humerus 
persisting. Some of these toothed birds were about as 
large as a pigeon; one was about three feet in height. 

Subclass III. — Ornithur^e (Modern Birds). 

In all living birds teeth are lacking and the tail is re- 
duced; and, excepting a few forms, all have well-developed 
wings. The recent subdivisions of the subclass are based 
upon characters not readily grasped by elementary stu- 
dents, so we must content ourselves with a classification 
founded on external features. The student should, how- 
ever, remember that the so-called orders are in no wise 
equivalent to orders in other groups of animals. 

Order I. — Struthii (Ostriches). 

The ostrich-like birds have long running legs, and wings 
so reduced as to be useless in flight, and with this the keel 
of the sternum (p. 354) has disappeared. The foot con- 
tains usually three, occasionally but two, toes. These 
birds are mostly large, and embrace the true ostriches of 
Africa, so valuable for their feathers; the South American 
nandus, the feathers of which are used for feather dusters; 
the emeus and cassowaries of Australia, and the nearly 
wingless kiwi of Australia. 



BIRDS. 



357 



Order II. — Kasores (Scratching Birds). 

These, like all the remaining birds, have a keeled sternum. 
They have a weakly curved beak, feet well fitted for run- 
ning, with three toes in front, and a fourth at a higher 




Fig. 151. — South American ostrich or nandu (Rhea americana). From Liitken. 

level behind. Here belong the grouse, the pheasants, and 
the domestic fowl and turkeys, as well as a considerable 
number of tropical forms. Our common hens, in all their 
numberless varieties, are descendants of the wild fowl of 
India. The turkeys are natives of America. 



358 



SYSTEMATIC ZOOLOGY. 



Order III. — Natatores (Swimming Birds). 

In these the short legs end in feet adapted for swimming 
by having a web between the anterior toes. The body 
varies greatly in shape. In the penguins (fig. 152) the 
wings have lost the powers of flight, the wing-feathers 
being short and scale-like. On the other hand, they are 




Fig. 152. — Penguin (Aptenodytes longirostris). From Liitken. 



strong swimmers, and the loons almost equal them in this 
respect. The other extreme is reached in those strong 
fliers, the albatross, tropic birds, gulls, etc. More useful 
to man are the ducks and geese, while the swans, auks, 
and cormorants must be mentioned as members of the 
order. 



BIRDS. 359 



Order IV. — Grallatores (Wading Birds). 

The wading birds have long legs, the tarsal region being 
extremely long, and the shank partly naked. Correlated 
with length of leg is length of neck. Here belong a long 
series of forms, some of which, like the snipe, are of value 




Fig. 153. — Wilson's Snipe (Gallinago wilsoni). After Wilson. 

to man as game-birds; while others, like the cranes, herons, 
storks, etc., have less importance. Some, like the ibis and 
the flamingo, are brightly colored, while marabou and 
egret furnish feathers for human adornment. 

In all the foregoing groups of birds the hinder toe is, 
as a rule, small and of little use. In all that follow it is 
usually well developed. 

Order V. — Raptores (Birds of Prey). 

The owls, hawks, eagles, and their allies are characterized 
by short, stout, curved beaks, strong feet and large wings ; 
all structures admirably adapted to the capture of prey 



360 SYSTEMATIC ZOOLOGY. 

and the tearing of flesh. Some, like the eagles, hawks, 
and vultures, are strong fliers with excellent powers of 
sight; the owls, on the other hand, are more dependent 
upon catching their prey by stealth; and their eyes are 
adapted to their nocturnal habits. The buzzards and vul- 
tures depend upon decaying flesh for their food, and their 
value as scavengers leads to their protection by law in 
the regions where they occur. 

In the birds of prey, like all that have preceded them 
in this account, the young, when hatched, are covered 
with feathers (usually down feathers), and have their 
powers well developed. In all the remaining orders the 
young are helpless and nearly naked when they escape from 
the shell. 

Order VI. — Columbine (Pigeons). 

The pigeons stand nearest to the Rasores from which? 
however, they differ in the weaker legs, the large pointed 
wings, and the fleshy membrane at the base of the beak, 
pierced for the nostrils. The five hundred different kinds 
of pigeons show little variety in form. Our domestic 
pigeons, with their wonderful variations, have descended 
from the rock-pigeon of Europe. The extinct dodo of the 
islands east of Africa was a flightless pigeon of large size. 
The species died out some two hundred years ago. 

Order VII. — Scansores (Climbing Birds). 

These birds have the feet adapted for climbing, two of 
the toes being directed forwards and two backwards. 
Some, like the toucans, have enormous bills, others have 
the beak of moderate size. Here belong the cuckoos, 
with their reprehensible egg-laying habits, and the well- 



BIRDS. 361 

known woodpeckers. The large group of parrots also 
belong to the group of climbing birds. In these last the 




Fig. 154. — Carolina Paroquet (Conurus carolinensis). After Wileou. 

tongue is fleshy, and the feet are very efficient organs of 
prehension. 

Order VIII. — Passeres (Perching Birds). 

In these the feet have three toes in front, one directed 
backward and all on a level, and no naked skin on the 
beak. They are usually subdivided into the Clama tores 
or crying birds, and the Oscines or singing birds, the latter 
having a complicated muscular apparatus in connection 
with the vocal organs. To the Clama tores belong the 
Asiatic hornbills, which recall the American toucans; the 
kingfishers, with their large strong beaks; and those gems 



362 SYSTEMATIC ZOOLOGY. 

of bird-life, the humming-birds. To the Oscines belong 
an enormous series of feathered songsters, the mere enume- 




Fig. 155. — Bird of Paradise (Paradisea apoda). After Levaillant. 

ration of which would take a volume the size of the present 
one, the whole series reaching its apex in that pestilential 



MAMMALS. 363 

immigrant, the English sparrow. Among these singing 
birds are some which, like the crows, are not noted for 




Fig. 156. — Winter Wren. From Coues. 

their musical abilities, and their near relatives, the birds 
of paradise. We can only mention, in addition, the star- 
lings, flycatchers, wrens, orioles, warblers, and thrushes, 
forms which make our woods and fields vocal and beautiful. 



Grade III.— MAMMALIA (Mammals). 

The name Mammalia is applied to all those forms which, 
like the mouse, cow, and man, have warm blood, a body 
covered with hair, and which bring forth living young, 
nourished during the early stages by milk secreted by the 
mother. These characters at once distinguish any mam- 
mal from any other animal, but other features of equal or 
greater importance occur. 

Hair occurs in the young of all mammals, and is usually 
found also in the adult; but in the case of the whales it is 
absent in the fully grown animal, and even in the young it 
is only found near the mouth. Hair is a product of the 
outer or epidermal layer of the skin. At places this layer 



364 SYSTEMATIC ZOOLOGY. 

dips down into the deeper layer {derma), forming a pit or 
follicle from the bottom of which the hair grows, continual 
additions being made at this point, commonly known as 
the 'root.' The hair itself is a solid column, varying con- 
siderably in shape in different animals, from the delicate 
fur of the fur-seal, to the bristles of the pig or the spines 
of the porcupine. There are usually glands present which 
open into the follicle and which secrete a fluid, the object 
of which is to keep the hair moist; and besides, each 
follicle is provided with muscles which serve to erect the 
hair at times of fright (as in cats and dogs) or in cold 
weather. 

Closely related to hair are nails, claws, hoofs, and horns.* 
In fact these structures must be regarded as hairs united 
throughout their length. At other times a similar con- 
solidation of hair gives rise to protective scales covering 
the body, as in the case of the pangolins (fig. 163). 

The bodies of the vertebrae usually have flat faces, and 
the vertebral column in most forms can be divided into 
five regions — cervical, thoracic, lumbar, sacral, and caudal. 
The cervical vertebrae bear no free ribs, and, except in 
three tropical species, they are constantly seven in number, 
the long-necked giraffe and the short-necked whale having 
the same number of cervicals. The thoracic vertebrae are 
more variable in number. They bear ribs, some of which 
extend downward and unite with the breast-bone or 
sternum. Between the thoracic and pelvic regions occur 
the ribless lumbar vertebrae, while the sacral vertebrae 
are those which unite with the pelvic bones. The caudal 
vertebrae are found in the tail. In the whales only cervi- 
cal and thoracic vertebrae can be distinguished, since the 

* Here are intended such horns as those of the cow, sheep, antelope, 
and rhinoceros; the horns of the deer are true bone. 



MAMMALS. 



365 



absence of a pelvis in these forms allows no line to be 
drawn between lumbar, sacral, and caudal regions. 

In the skull there is a tendency for bones which are 
distinct in the fishes and reptiles to fuse with each other, 
so that the number of distinct elements is considerably 
reduced. The skull is borne on the first cervical vertebra 
(atlas) upon which it slides by means of two rounded sur- 
faces or condyles. The lower jaw articulates directly with 
the skull, and is never suspended by a quadrate bone, as 
in all other classes of vertebrates, the cyclos tomes excepted. 




Fig. 157. — Brain of dog. 



(After Wiedersheim.") II-XII, the cranial nerves 
(see page 299). 



The fore limbs are always present; the hind limbs are 
absent in the whales and manatees, being represented in a 
few forms by one or two bones imbedded in the muscles of 
the trunk. Except in the Monotremes (p. 369), the cora- 
coid does not occur as a distinct bone, but as a small 
prominence joined to the shoulder-blade (scapula), while 
in many the collar-bone (clavicle) also is lacking. The feet 
have typically five toes, but not infrequently this number 
is reduced by a disappearance of the outer digits, the 
reduction reaching its extreme in the cow, which has but 
two, and the horse, which walks upon the tip of its middle 
toe. 



366 SYSTEMATIC ZOOLOGY. 

The most marked characteristic of the nervous system 
is the great relative increase in size of the cerebrum, and, 
to a less extent, of the cerebellum; the optic lobes and 
the medulla, so prominent in the lower forms, being over- 
shadowed by these parts. The cerebrum is the seat of 
intelligence, and this increase in size is correlated with 
the higher mental powers of the mammals. Microscopic 
study of the brain shows that this organ is composed of 
two different portions, called, according to their colors, 
white and gray, and that the gray matter is the true brain 
substance, while the white is composed of nerve-cords to 
transmit nerve impulses. The gray matter is on the 
outside of the cerebrum, hence the larger the brain the 
more surface it has, and consequently the more gray 
matter it can have. In the higher mammals the amount 
of surface of the cerebrum is greatly increased by folds 
or convolutions, and the extent and complexity of these 
convolutions correspond well with the intelligence of the 
form. 

In the eyes the nictitating membrane or 'third eyelid' 
of the birds is reduced to a small fold at the inner angle of 
the eye (p. 303). Except in the whales, and some seals, 
moles, etc., external ears are developed, while the internal 
parts of the ear become considerably modified. Thus the 
quadrate and one other bone pass in to the middle ear, 
where they, together with a third bone (stapes), form a 
chain to convey sound-waves to the sensory portions. 
In the inner or sensory portion a spiral outgrowth, the 
cochlea, occurs (fig. 112), and in this is a most wonderfully 
intricate sensory apparatus — the organ of Corti — the func- 
tions of which are as yet uncertain. 

The mouth is usually provided with fleshy lips, and all 
mammals, except monotremes, some edentates and whales, 



MAMMALS. 



367 




Fig. 158. — Milk (shaded) and perma- 
nent dentitions (outline) of the cat. 
c, canines; p^-p 4 , premolars; m, 
molar. The incisors (to left) not 
lettered. From Boas. 



have teeth. These teeth are always confined to the 
edges of the jaws (cf. 
Fishes, p. 24), being in- 
serted by one or more roots 
into sockets in the bone. 
Some mammals have but a 
single set of teeth through- 
out life, but the majority 
have a first or milk dentition, 
which is soon lost and re- 
placed by a permanent den- 
tition. Occasionally, as in 
the sperm-whale, etc., all the 
teeth are similar in shape, 
but usually several different 

kinds occur, the extreme being reached when four types 
are present — incisors, canines, premolars, and molars. 
The incisors have but a single root, and are found in the 
premaxillary bone and in the corresponding position in 
the lower jaw. The first teeth in the maxillary, if single- 
rooted and pointed, are called canines; and behind these 
come the molars, with two or more roots. These in turn 
are subdivided into premolars (the bicuspids of the dentist) , 
which appear in both milk and permanent dentitions, and 
molars proper, which occur only in the permanent set. 
The number of teeth and their arrangement vary con- 
siderably in different mammals, and the characters which 
they furnish are of great value in grouping the various 
species. To express these characteristics briefly a dental 
formula has been introduced, in which the different kinds 
of teeth are indicated by initials, while the number in 
each half of either jaw is represented by a figure above or 
below a horizontal line. Thus the permanent dentition of 



368 SYSTEMATIC ZOOLOGY. 

man is expressed thus: if, i, /w&f, raj; which indi- 
cates that in man there are two incisors, one canine, two 
premolars, and three molars in each half of each jaw. The 
pig has, H, c\, praf, raj; the cow, i%, cf, praj, raj, 
incisors and canines being absent from the upper jaw. 

The body-cavity is divided by a transverse muscular 
partition, the diaphragm (p. 309), into two chambers — an 
anterior pleural cavity containing the heart * and lungs, 
and a posterior peritoneal cavity in which are situated the 
stomach, liver, intestine, etc. 

The heart, placed a little to the left of the median line, 
is four-chambered, having, like that of the birds, two 
auricles and two ventricles. Of these the auricle and ven- 
tricle of the right side receive the blood from the body and 
send it to the lungs, while those of the left side take the 
blood as it comes from the lungs and send it through the 
aorta to all parts of the body. The> aorta, which bends 
backward and to the left, represents the left arch of the 
fourth pair of the primitive branchial vessels, the right of 
the same pair being partially represented in the artery 
(subclavian) , which carries the blood to the right fore limb 
— a condition just the reverse of what occurs in the birds. 
The sixth pair of arches form part of the arteries (pulmo- 
naries) which convey blood from the heart to the lungs. 
The blood of the mammals differs from that of all other 
fo ms in that the red corpuscles (p. 314) are usually cir- 
cular in outline and are not nucleated. 

The monotremes form the only exceptions to the state- 
ment that the mammals bring forth living young. They 
lay eggs, one species having the eggs about the size of a 
pigeon; but the young which are hatched from these eggs 

* The heart, inside the pericardium, is not actually inside the 
pleural cavity, which really contains the lungs alone. 



MAMMALS. 369 

are nourished by milk secreted by the mother, as in the 
case with all other mammals. 

The Mammalia are divisible into two classes: Mono- 
tremata and Eutheria. 

Class I.— MONOTREMATA. 

This class contains three or four species of animals 
which are found only in Australia and its immediate 
neighborhood. They present resemblances to the birds, 
or, better, to the reptiles, in the following points in all of 




Fig. 159. — Duckbill (Ornithorhynchus paradoxus). From Liitken. 

which they differ from the other mammals: They lay 
eggs; they have well-developed coracoid bones; the 
bones of the skull are fused, as in birds, and reproductive 
and excretory organs empty into the posterior portion 
(cloaca) of the intestine, and thence pass by a common 
opening to the exterior. 

The monotremes include the duckbill (fig. 159) and the 
spiny ant-eaters. The duckbill is an aquatic animal, and 
receives its common name from the fact that it has a 



370 SYSTEMATIC ZOOLOGY. 

horny bill much like that of the duck. It lives in burrows 
in the banks of streams, and feeds on beetles, shrimps, 
etc., which it catches in the water and crushes with its 
horny teeth, its true teeth being lost at an early age. The 
spiny ant-eaters resemble the duckbill in their burrowing 
habits, but they live exclusively on the land, where they 
feed on ants. They are, like the true ant-eaters (p. 374), 
entirely toothless, and receive the adjective spiny of their 
common name from the fact that their hair takes the 
shape of long stout spines, recalling those of the porcupines. 

Class II.— EUTHERIA. 

This division contains the great majority of the mam- 
mals and is characterized by the following features : The 
alimentary canal opens to the exterior distinct from the 
reproductive and excretory organs, the sutures of the 
skull are well marked and the coracoid bone is reduced 
and fused with the shoulder-blade, forming the coracoid 
process of human anatomy. The Eutheria are divided 
into twelve orders: Marsupialia, Edentata, Rodentia, 
Insectivora, Chiroptera, Cetacea, Sirenia, Proboscidea, 
Hyracoidea, 'Ungulata, Carnivora, and Primates. 

Order I. — Marsupialia. 

This order receives its name from the fact that in the 
female a curious pouch or marsupium is developed on 
the lower surface of the body, in which the young are 
placed by the mother immediately after birth, and where 
they remain until able to take care of themselves. This 
pouch is supported by a pair of bones which extend for- 
ward from the pelvis — the marsupial bones (fig. 160) — 
and these, as well as a peculiar inbending of the angle of 



MAMMALS. 



371 



the lower jaw, serve at once to distinguish any marsupial 
skeleton. The living marsupials have a peculiar distribu- 
tion: they are restricted to warmer America and the chain 
of islands extending from Australia to the Celebes. Fossil 
forms are found in Europe as well. 

The North American species are all opossums — forms 
with prehensile tails which have given rise to the expres- 
sion 'playing 'possum/ from their habit of feigning death 





Fig. 160. — Pelvis of Opossum. (After 
Minot.) M, marsupial bone; il, 
ilium; is, ischium; p, pubis. 



Fig. 161. — Opossum (Didelphys vir- 
giniana). After Audubon and 
Bachman. 



when disturbed. Their food is chiefly insects, but birds, 
eggs, etc., are not despised. 

Australia is the real home of the marsupials; indeed, at 
the time of its discovery this continental island contained 
only marsupials, if we except mice and the dingo, or 
native dog. In this region are found forms which recall 
animals of different groups occurring in other parts of the 
world. Thus the wombat resembles in size and teeth the 
beaver; the thylacines in habits and in form are dog-like, 
while the phalangers in size and appearance arc like the 
flying squirrels, and, like those animals, they have that 
same fold of skin which enables them to glide through the 



372 SYSTEMATIC ZOOLOGY. 

air from tree to tree. Most familiar of all the Australian 
forms are the large grass-eating kangaroos, in which the 
fore legs have become almost useless for locomotion, the 
animal jumping with its hind legs,, and, when resting, 
supporting itself upon these members and its enormously 
developed tail. There are also fossil marsupials in Aus- 
tralia, some of them of enormous size. Thus Thylacoleo 
was as large as a lion, while Diprotodon had a skull three 
feet in length and a thigh-bone two feet from tip to tip. 

The remaining orders of mammals were formerly placed, 
in contrast to the Marsupials, as a distinct group, Placen- 
talia, from the fact that they are not born until their 
internal organization has been well advanced; and in 
order that they may be supplied with nourishment a 
peculiar vascular structure is formed, — the placenta, — 
by means of which blood is brought to the growing em- 
bryo. It has, however, been ascertained recently that 
some of the Marsupials also have a placenta, and with this 
discovery the line of course breaks down. 

Order II. — Edentata. 

The edentates, the lowest of the placental mammals, 
receive their name from the fact that incisor teeth are 
always lacking, while in the ant-eaters no teeth occur. 
The feet are armed with strong claws. The group is a 
tropical one, and has its greatest representation in Amer- 
ica. Here belong the armadillos, in which the deeper 
layer of the skin becomes converted into bone, forming 
an armor over the body. In the fossil Glyptodon this 
armor formed one solid piece, enclosing the trunk much like 
the armor of a turtle; but in the living forms it becomes 



MAMMALS. 



373 



broken into several transverse bands, which move upon 
each other, so that the animal can coil itself into a ball. 

The sloths are larger forms which, back downward, 
crawl with the slowest motions along the branches of the 




Fig. 162. — Nine-banded Armadillo (Dasypus novemcinctus). From Liitken. 

trees, holding themselves by their hook-like claws. Upon 
the ground they walk with difficulty, their long claws 
being in the way. In geological times there were forms 




Fig. 163. — Pangolin (Manis longicaudata). From Monteiro. 

allied to the sloths, but of much larger size. One, the 
Megatherium of South America, had a skeleton 18 feet in 
length. Another form, Mylodon, found in North America 



374 SYSTEMATIC ZOOLOGY. 

receives interest from the fact that it was first described 
by Thomas Jefferson. 

The ant-eaters are true edentates in that they are 
wholly without teeth. As their name implies, ants form 
the chief part of their food; their claws are well adapted 
for digging into the nests , the tongue is very long and 
extensible, while the salivary glands pour out a thick, 
sticky secretion which fastens the ants to the tongue. 
The true ant-eaters are natives of South America, but in 
Africa and India are allied forms with teeth, which also 
feed upon ants. Among these are the pangolins (fig. 163) 
in which the whole upper surface of the body is covered 
with scales, arranged somewhat like those of a pine-cone. 
These scales, as already mentioned (p. 364), are to be 
regarded as modified hair. 

Order III. — Rodentia (The Gnawers). 

The rodents are the gnawers, the well-known abilities of 
rats, mice, and beavers in this direction being shared by 
all members of the order. They have no canine teeth; 




Fig. 164. — Skull of muskrat (enlarged), showing the gnawing incisors and 
absence of canines. 

the molars are usually f, while the incisors vary between 
|, |, and f . These incisors demand a moment's attention. 
These teeth have persistent pulps, i.e., they continue to 
grow throughout life. As fast as they wear away they 



MAMMALS. 375 

are renewed from below. In each incisor two parts can 
be distinguished: the anterior face of the tooth is covered 
with a very hard layer {enamel), while the posterior sur- 
face is composed of a much softer dentine. This dentine 
wears away much faster than the enamel, and the result 
is that the teeth are constantly kept at a chisel-edge. 

Lowest of the rodents come those forms familiarly 
known as hares and rabbits, with disproportional hind 
legs and long ears. The distinction between the two — 
hares and rabbits — is very slight, the true rabbit being a 
native of southern Europe. All the rest are hares. In 
America, however, the term rabbit is usually restricted 
to the small burrowing forms. 

The porcupines, with some of their hair changed to long 
sharp spines, — efficient weapons of defence, — come next. 
These occur in both hemispheres, but the American forms 
are mostly arboreal, while those of the Old World burrow. 
Allied to them in structure, but differing in fur, are the 
chinchilla and the coypu of South America, the latter fur- 
nishing the well-known ' nutria fur.' The same country 
furnishes the stupid, so-called guinea-pigs, — whose young 
shed their milk-teeth before birth, — and the giants of 
rodents, the capybara, with a body four feet in length. 

Rats and mice are the great pests of the order. Our 
common brown rat is a recent immigrant. The early set- 
tlers brought with them the black rat, the brown rat being 
then unknown in western Europe, but about 1720-30 the 
latter came west from the Volga region, and gradually 
spread all over western Europe and then over America, 
the black rat disappearing before the invader. There are 
many rat-like forms, among them the lemmings of the 
Arctic regions, vast hordes of which occasionally overrun 
Norway; the dormice, which hibernate in winter; the 



376 SYSTEMATIC ZOOLOGY. 

gophers and pocket-rats, which burrow through the soil in 
the western states; the familiar muskrat, and the less 
familiar jumping mice, which resemble the kangaroos in 
their locomotion. 

Another series of rodents contains the beaver, common 
to the Old World and the New, which furnishes furs of 
great value. These live most of their lives in the water, 
building dams so that they may always have plenty of 
it; while their near relatives, the woodchucks, and their 
western representatives, the prairie-dogs, have no such de- 
pendence upon water. Highest of all the rodents are 
the ground-squirrels, the true squirrels, and the flying 
squirrels. 

Order IV. — Insectivora (Insect-eaters). 

These are small mammals, in which all four types of 
teeth are developed, and which are marked off from all 
other orders by characters rather difficult of expression. 
As their name implies, they feed largely upon insects, but 
worms and other small animals are not despised. The 
species are largely tropical, but the shrews and moles are 
found in cooler climates. Most of the species are noctur- 
nal and burrowing animals, consequently their eyes are 
small and degenerate while their fore legs are adapted for 
digging. 

Order V. — Chiroptera (Bats). 

The bats are the only mammals which truly fly. In the 
case of the flying squirrel and the rest, the animals glide 
through the air on the plane formed by the lower surface 
of the body, the tail, and the broad membrane which 
extends between the limbs; and they can never ascend to 
the level from which the flight started. With the bats, 



MAMMALS. 



377 



on the other hand, there are no such limitations to the 
flight. The wing in the bats consists of a very thin mem- 
brane supported upon a framework composed of the body 
and the bones of the fore limbs. These latter are elon- 
gated, four of the fingers excessively so (fig. 165); and 




Fig. 165. — Skeleton of bat. 

between these fingers and extending back to the body and 
the hind limbs is the web of the wing. The thumb, how- 
ever, is not involved in the wing, but forms a claw of great 
use in supporting the body, although when at rest they 
usually hang, head downwards, by the five claws of the 
hind feet. The jaws are provided with incisors, canines, 
premolars, and molars. Bats are social animals, occur- 
ring in large numbers in caves, deserted buildings, and 
the like, where they spend the day, and it is remarkable 
that these colonies are usually entirely male or female. In 
a rough way the bats may be divided into fruit-eating and 
insect-eating forms, their habits being correlated with 



378 SYSTEMATIC ZOOLOGY. 

peculiarities of structure. To the fruit-eating species 
belong the large bats of the East Indies known as flying 
foxes. All of our bats are insect-eating. Some of the 
South American bats (not the one called the vampyre by 
Linne) are known to suck the blood of other mammals. 

In the five orders Marsupials, Edentates, Rodents, In- 
sectivores, and Bats the surface of the cerebrum is smooth; 
in all the remaining orders it is at least fissured, and in 
most it is convoluted (see fig. 157), this increase in sur- 
face reaching its greatest development in man. Since 
this line of division corresponds in a way with the intelli- 
gence of the forms (see p. 366), the five orders already 
mentioned are grouped together as Ineducabilia ; the 
others- are associated as Educabilia. 

Order V. — Cetacea (Whales). 

The whales have a fish-like body, the resemblance being 
frequently heightened by the development of a dorsal fin; 
and yet in all points of structure they are mammals. The 



Fig. 166. — Pigmy whale (Kogia floweri). From Gill. 

anterior limbs contain the same bones (except that the 
number of joints in the fingers may be increased) as do 
our own, but the whole has been modified into a 'flipper' 
for use in swimming. The hind limbs are absent exter- 
nally, but imbedded in the flesh on either side is a bone, 



MAMMALS. 379 

variously interpreted as a part of the pelvis or as the bone 
of the thigh. The body terminates in a bilobed caudal 
fin (' flukes'), but this, instead of being vertical, as in the 
fish, is horizontal. All of the whales have teeth in the 
young stages; some retain them through life, while others 
lose them long before maturity, sometimes even before 
birth. The stomach is remarkable for having several 
(4-7) chambers, this complication recalling the condition 
in the cow (see p. 385). 

According to the presence or absence of teeth the living 
whales are divided into two groups. In some of the 
toothed whales but two teeth are present; others .may 
have a large number; and usually these cannot be well 
distributed among incisors, canines, etc., as all are essen- 
tially alike in size and shape. In the male narwal, how- 
ever, one of the upper teeth on one side (apparently a 
canine) grows straight forward into a long twisted spear 
eight or nine feet in length, while the other teeth disap- 
pear at an early age. The killer-whales are compara- 
tively small, but are among the most voracious of mam- 
mals, not hesitating to attack the largest whales. Here 
also belong the blackfish, porpoises, and dolphins. The 
sperm-whales are larger, and have no teeth in the upper 
jaw, while the lower jaw is abundantly supplied. They 
derive their common name from the spermaceti which 
they produce. This is a solid granular substance found 
in the 'case/ a cavity occurring on the right side of the 
front of the head between the skin and the skull. The 
sperm-whales also produce the substance known as am- 
bergris used in perfumery. This is a concretion formed 
in the intestine and is found floating on the surface of 
the sea. It is worth about $20 a pound. 

The toothless whales are also known as whalebone whales, 



380 



SYSTEMATIC ZOOLOGY. 



from the fact that they bear upon the lower sides of the 

upper jaw hundreds of long 
parallel plates of so-called 
whalebone or baleen. These 
plates are fringed at the end, 
and the whole apparatus forms 
an efficient strainer, used in 
separating the small animals 
upon which these whales feed 
from the surrounding water. 
haifo^whaie^BS It ■ among these whalebone 
oWaXW^r'Ktf whales that the giants among 
&£S£2£ft£& The tme mammals occur. The right 

whales of the Arctic seas 
reach a length of sixty feet, the razor-back whales are 
still larger, while the sulphur bottoms and silver bottoms 
(so called on account of the color of the lower surface) 
attain a length of from 90 to 95 feet. 




Fig. 167. 



Order VII. — Sirenia (Sea-cows). 

These are whale-like animals, with the same nippers and 
the same horizontal tail, but they differ from the whales in 
the possession of an evident neck, and of sparse hair or 
bristles all over the body. Besides these features all, 
except the extinct Rytina, have flat-crowned molar teeth. 
The living forms are very few. Rytina, which lived near 
Bering Strait, was exterminated in the last century. The 
dugong is the representative of these forms in the Indian 
Ocean, while the three species of manatees come, one 
from Africa, the other two from the eastern coasts of 
America (fig. 168). All the sea-cows are vegetable 
feeders, living upon seaweed or, in the case of the manatees, 
upon the plants found in fresh-water streams as well 



MAMMALS. 



381 



Order VIII. — Proboscidia (Elephants). 

The elephants are the giants among the land mammals. 
They have five toes, each encased in its own hoof; they 




Fig. 168. — A manatee (Trichechits americanus) feeding. After Elliott. 

have no incisors in the lower jaw, while the pair in the 
upper jaw are developed into large tusks. Canines are 
lacking, but there are seven molars in each half of each 



382 SYSTEMATIC ZOOLOGY. 

jaw. These molars are fiat-crowned, the surface of the 
crown being crossed by several ridges of harder enamel. 
Only two, or at most three, of these molars are in use at 
once, but as the old ones wear out they drop out at the 
front of the jaw, and are replaced by new ones from behind 
until the seven are gone. The skull is enormous, but it is 
comparatively light on account of the numerous cavities in 
the bone. Most striking of all is the proboscis, which is 
merely an enormously developed nose, with capacities 
which only one who has studied an elephant can realize. 
The skin is almost entirely naked, hairs being scarce, and 
on the tail taking the shape of long wiry bristles. 

To-day two species of elephants exist, one having its 
home in India, the other in Africa. In the later geological 
ages there were several others, one, the mammoth, having 
lived in America and others in Europe. Towards the 
end of the eighteenth century remains of hairy elephants — 
even the flesh being preserved — were found imbedded in 
the ice in northern Siberia. Another has recently been 
found equally well preserved. Allied to the elephants were 
the somewhat larger mastodons, in which the molar teeth 
bore conical cusps, while the tusks were frequently enor- 
mous. Some mastodons had incisors in the lower jaw 
as well. 

Order IX. — Hyracoidea (Coneys). 

This order contains but two or three species, distributed 
from Syria south into Africa. In having long curved 
incisors and absence of canines they recall the rodents; 
in other points their structure is like that of the rhinoceros,, 
while the foot-pads on their feet recall those of the cat or 
dog. The Hyrax of Syria is probably the coney of the 
Old Testament. 



MAMMALS. 



383 



Order X. — Ungulata (Hoofed Animals). 

To this order belong the great majority of important 
mammals. They are herbivorous, usually of large size, 
and lack collar-bones. The feet are used solely in walking, 
and not in prehension, each toe having its tip enclosed in 
a horny hoof, and in living forms there are never more 
than four toes developed on a foot. The living ungulates 




Fig. 169. — Sumatran rhinoceros (Rhinoceros sumatrensis). From Liitken. 

are arranged in two series, according to the number — even 
or odd — of toes upon their hind feet. The odd-toed 
forms are called Perissodactyla, the even-toed are 
Artiodactyla. 

To the perissodactyls belong, of living forms, the tapirs, 
rhinoceroses, and horses. The tapirs live in the forest 
regions of the tropics of both continents. They have a 
hog-like body, large prehensile upper lip; teeth, if ; c\, 
praf, mf ; while their fore feet have four toes, the hind 
feet three. Yet, although the fore feet have an even 
number of toes, these are not symmetrically arranged, 



384 



SYSTEMATIC ZOOLOGY. 



as in artiodactyl forms, the pig for example, but one (third) 
is enlarged and bears most of the weight of the body. 

The rhinoceroses have three toes on each foot; the skin 
is extremely thick;* the snout bears one or two well- 
developed horns, in which there is no bony core; and 
canine teeth are not developed even in the young. There 
are six species known, those occurring in Africa having 
two horns, while in the East Indies are both one- and two- 
horned forms. 

In the horses the reduction of toes has gone still farther, 
there being but one (the middle or third) in each foot. In 
. . the skeleton, however, traces of two more can 

be found in the 'splint-bones/ two small 
bones occurring alongside the large 'cannon- 
bone ' (fig. 170). All of the existing horse- 
like forms have the teeth tf, c{, p£, raf, 
and all are natives of the Old World, none 
existing in America at the time of its dis- 
covery. All evidence goes to show that 
the home of the domestic horse was in cen- 
tral Asia, and indeed four different species 
of horse run wild there to-day. The asses 
have their centre around the eastern end 
of the Mediterranean, while the zebras or 
striped horses are all African. In geological 
time, however, America had horses, and 
the fossils in our western states give the 
history of the race from small forms about 
the size of a fox, and with three toes behind 
and four in front; later, those as large as a 
sheep, with three functional toes in each foot; and still 

* The elephants and rhinoceroses were formerly united as a group 
called Pachydermata on account of the very thick skin. 





Fig. 170.— Foot 
of horse, 
showing the 
splint - bones 
(second and 
fourth toes) 
at s; 3, third 
toe. 



MAMMALS. 



385 



later, three-toed forms as large as a donkey. In domesti- 
cation horses vary extremely in size as in other respects. 

Lowest of the artiodactyls, or even-toed ungulates, come 
the two species of hippopotamus, in which there are four 
toes, large canine teeth, and a huge, clumsy body, some- 
times fourteen feet in length. In the pigs the canines 
are still large, and the toes are four in number, but the 
outer ones are lifted above the ground so that they are 
useless as organs of locomotion. Our domestic swine have 
descended from the wild boars of Europe. In the warmer 
parts of America the peccaries represent the group. 

The hippopotamus and the pigs have the axis of the 
foot passing up between the middle toes ; in other words, 
they have cloven hoofs. In 
all other artiodactyls the 
cloven hoof occurs, and be- 
sides, they chew the cud, 
and hence they are asso- 
ciated as a group of rumi- 
nants. The stomach is di- 
vided into four chambers, 
and when a cow, for instance, 
feeds, it swallows the grass 
without chewing it. It 
passes down to the first 

stomach and thence to the second. In these it becomes 
mixed with digestive fluids and softened. It is then 
brought up in the mouth, thoroughly chewed, and again 
swallowed. This time it passes into the third stomach, 
and from this into the fourth, and so into the intestine. 

To the ruminants belong the most valuable domesti- 
cated animals. In South America are found the llamas 
and alpacas, which were the cattle and beasts of burden 




Fig. 171. — Diagram of the stomach 
of a ruminant. The dotted line 
shows the course of the food. 



386 SYSTEMATIC ZOOLOGY. 

of the ancient Peruvians; while in Asia and Africa the 
camels, in part, take their place. Two kinds of camels 
occur, one with one and the other with two humps upon 
the back. These humps are merely large masses of fat. 
Some fifty years ago the United States Government intro- 
duced some camels into our southwestern territory, and 
the descendants of these are still to be found in Arizona. 

We associate together under the common name of deer 
all those ruminants which have horns consisting of solid 
bone. These horns are annually shed and grow out anew 
each year, usually increasing in size with the age of the 
animal. When first formed the horns are covered with a 
thin skin with short hairs. The horns in this condition 
are said to be 'in the velvet.' When the horn is fully 
formed the skin dies and is worn off. In some deer horns 
are borne only by the male, but sometimes both sexes, as 
with the reindeer, are provided with them. The long- 
necked giraffes are closely related to the deer. 

In other ruminants the horns are never shed. In these 
the horns consist of a central core of bone, covered on the 
outside with a horny structure — in reality modified hair 
(p. 364). Here belong our domestic cattle, which are 
believed to have arisen from four different species, which 
formerly were wild in Europe. This wild stock is almost 
extinct. One of these forms at least was closely similar to 
our American bison, which has so nearly approached ex- 
tinction from the desire for 'buffalo* robes. The true 
buffalo are all natives of the Old World, and occupy a 
position between the ancestors of domestic cattle and the 
long series of forms grouped together as antelope, most of 
which belong to Africa, but which are represented in 
America by the prong-horned antelope of our western 
states (fig. 172) which forms the sole exception to the 



MAMMALS. 387 

statement that the antelopes do not shed their horns. 
Other members of the same group with permanent horns 
are the sheep and the goats, the series ending with the 
so-called musk-ox of the arctic regions, a form nearer 
the goats than to the domestic cattle in its structure. 

As a whole, we may say that in points in structure — 
especially in the characters of feet and teeth — the group 
of ungulates is among the most specialized of the mam- 




Fig. 172. — Prong-horned antelope (Antilocapra americana). 

malia, the whales, bats, seals, and possibly the elephants 
alone excelling them in this respect. 

Order X. — Carnivora (Beasts of Prey). 

The beasts of prey are specialized in the direction of 
flesh-eating. Their bones are slender, but strong; their 
feet (usually five-toed) are furnished with claws; while on 
the top of the skull is a crest for the attachment of the 



388 SYSTEMATIC ZOOLOGY. 

strong muscles of the jaws. All four kinds of teeth are 
present, and one of the molars or premolars is flattened 
vertically, so that, meeting its fellows of the opposite jaw, 
it cuts like a pair of shears. In the lower mammals we 
find the lower jaw so hinged upon the skull that it can 
move back and forth in grinding the food. In the car- 
nivores, on the other hand, no such motion is possible. 

The carnivores are divided into two groups, one embrac- 
ing the typical land-inhabiting forms; the other, which 
includes the walrus and the seals, is modified for an aquatic 
life; the differences being most marked in the structure of 
the appendages. In the first group the legs are elongate 
and the toes are distinct, whence the name Fissipedia; 
while in the other division (Pinnipedia) the legs are 
shortened, the fingers are webbed, and the feet are thus 
effective paddles. 

Lowest of the Fissipedia are the bears and their allies, 
in which the whole sole of the foot is applied to the ground 
in walking, and hence are called plantigrade, in opposition 
to those digitigrade forms, like the cat and dog, which walk 
upon the tips of their toes. The bears are widely dis- 
tributed over the earth, America having at least three 
species. The raccoon is distributed throughout the 
United States, and in tropical America is represented by 
that exceedingly interesting animal, the coati. 

Another group of carnivores includes the otters, mink, 
ermine, sable, and marten — all of which are valuable for 
the furs which they afford, — as well as the weasels and 
ferrets, and the well-known skunks. These are partly 
plantigrade, partly digitigrade. 

The dogs, foxes, wolves, and jackals are all digitigrade. 
They have the teeth, if, c\, pmf-, raf or f. Foxes and 
wolves are wild, and many believe that our domestic dogs 



MAMMALS. 



389 



have descended, from some wolf stock; but others think 
that dogs and wolves are distinct, and even that our com- 
mon dogs represent several originally distinct kinds or 
species. 

The hyaenas are intermediate between the cats and dogs 
in many respects. They have the back teeth fitted for 

- A. \ 




Fig. 173. — The harbor seal (Phoca vitulina). After Elliott. 

crushing. In the cats, of which there are more than fifty 
species, the teeth are usually £}, c\, pm-f, m\, while the 
claws are retractile into sheaths. Our domestic cat appar- 
ently had its origin in Egypt, while ancient Greece and 
Rome lacked our familiar puss, its place being taken by 
domesticated martens. Among the cats the tiger, lion, 
panther, leopard, and puma rank first, and with them are 
associated the wildcats and lynxes. 

In external form the Pinnipedia (seals and walruses) have 
little resemblance to the other carnivores, but in structure, 



390 SYSTEMATIC ZOOLOGY. 

and especially in their skulls, there is great resemblance to 
the bears and otters in particu ar. As has been said, their 
feet are modified into paddles, and only the distal region 
is distinct from the body. Lowest are the large walruses, 
of which there are two species in northern seas, in which 
the upper canines are enormously developed. They can 
use their hind feet in walking. The eared seals are so- 
called because they have small external ears. The largest 
of these are the sea-lions, but the most valuable are the 
fur seals, of which two species are known. The one which 
occurs in the southern hemisphere has been almost 
exterminated, while the Alaskan species is rapidly follow- 
ing the same road. 

The true seals lack all external ears, and since their skins 
are less va uable, a longer lease of life seems assured them. 
They occur on all shores, and from their fish-eating habits 
are frequently a nuisance to fishermen. 

Order XL — Primates. 

The term Primates is given to that group which includes 
the monkeys, apes, and man, from the fact that they are 
the first or highest group in the animal kingdom. Collar- 
bones are always present; the feet are very primitive, and 
the fingers and toes are armed with nails, claws but rarely 
occurring. Intelligence, not structure, assigns them the 
leading place. 

Lowest come the group of lemurs or 'half apes/ which 
have their metropolis in Madagascar, but have relatives in 
Africa and in the East Indies. They are largely nocturnal, 
and eat fruit or insects or other small animals. They are 
noticeable from the fact that the second finger is pro- 
vided with a claw. 



MAMMALS. 391 

The marmosets are small squirrel-like forms found in 
South America. They are provided with claws on all 
digits except the great toe, and the tail is incapable of 
grasping, while the thumb is scarcely capable of being 
opposed to the fingers. 

The remaining American monkeys — the howlers, sapa- 
jous, spider-monkeys, and the like — have a broad septum 




Fig. 174. — Chimpanzee (Troglodytes niger). After Brehm. 

of the nose, causing the nostrils to be wide apart; the 
thumb is scarcely opposable, and in some is lacking ; while 
the teeth differ from those of the Old World monkeys, 
and of man, in having pm-f . Many have a prehensile tail. 
The Old World monkeys have the nostrils closer together, 
the thumb as well as the great toe is opposable, and the 
tail never takes the place of a fifth hand. In their teeth 
they resemble man: if, c\, pm^, mf. The baboons, 
distributed across Asia and Africa, have large cheek 



392 SYSTEMATIC ZOOLOGY. 

pouches for the storage of food, etc., and naked callous 
patches on which they sit. Some have long tails, others 
no tails at all. The macaques and mangabeys are allied 
Asiatic forms. 

In the anthropoid apes tail, cheek-pouches, and callous 
spots are lacking; as the name indicates, they are man- 
like. There are three of these. The orang-utan (the 
name is Malay for Man of the Woods) lives in Borneo and 
Sumatra. The chimpanzee and the gorilla are African. 
Each of these has certain points in which it is more like 
man than are the others. 

The highest mammal is man, who differs from the other 
primates less in structure than in intelligence. 



Summary of Important Facts. 

1. The CHORD ATA possess a notochord, gill slits, and 
a central nervous system entirely on one side of the diges- 
tive tract. 

2. To the Chordata belong the Tunicata, Leptocardii, and 
Vertebrata. 

3. The TUNICATA are marine; in most species the noto- 
chord exists only in the tadpole-like young. Many species 
reproduce by budding. 

4. The LEPTOCARDII are fish-like, but differ from the 
true fishes in lack of skull, vertebrae, and heart. They are 
marine, small, and transparent. 

5. The VERTEBRATA have skull and vertebral column, 
and usually paired appendages. They breathe by gills 
or by lungs, both connected with the digestive tract. 

6. The brain consists of five divisions : cerebrum, 'twixt- 
brain, optic lobes, cerebellum, and medulla oblongata. 
7. The heart is ventral in position; it consists of an 



MAMMALS. 393 

auricle and a ventricle. In air-breathing vertebrates the 
auricle is, and the ventricle may be, divided. 

8. The sexes are usually separate, and reproduction by 
budding, etc., is unknown. 

9. The Vertebrata are divided into the Cyclostomata 
and the Gnathostomata. 

10. The Cyclostomata lack true jaws and paired ap- 
pendages; they have a single nostril. Some are parasitic. 

11. The Gnathostomata have true jaws and paired 
nostrils. 

They are subdivided into Pisces, Amphibia, Reptilia, 
Aves, and Mammalia. 

12. The Pisces or Fishes have median and usually paired 
fins; they usually have scales; they breathe by gills and 
have a two-chambered heart. 

13. The Pisces are divided into Elasmobranchii, Ga- 
noidei, Teleostei, and Dipnoi. 

14. The Amphibia usually have true feet; they have 
lungs, and in the young gills as well. A metamorphosis is 
common. The heart is three-chambered. 

15. The Amphibia are divided into the Caecilia, Urodela, 
and Anura. 

16. Pisces and Amphibia are called Ichthyopsida on 
account of their gills and their aquatic life. 

17. Reptilia have external scales and a three- or four- 
chambered heart; they lack functional gills at all times. 

18. Recent Reptiles are grouped as Lacertilia, Ophidia, 
Testudinata, and Crocodilia. 

19. Aves or Birds are characterized by the presence of 
feathers, a four-chambered heart, warm-blood, and wings. 

20. Birds and Reptiles are grouped as Sauropsida on 
account of the single occipital condyle, the similar scales and 
the large eggs. 



394 SYSTEMATIC ZOOLOGY. 

21. The Mammalia have hairy skin, a four-chambered 
heart, warm blood, and two occipital condyles. 

22. The young are nourished by milk furnished by the 
mother. 

23. The teeth have roots, and usually several kinds of 
teeth are recognizable. 

24. The Mammals are divided into Monotremata and 
Eutheria. 



GENERAL ZOOLOGY. 

The foregoing pages have been largely devoted to the 
study of the structure of animals and the various degrees of 
structural resemblances which they bear to each other 
as expressed by classification. Animals, however, pre- 
sent other points for consideration, and some of these 
may be referred to here. 



COMPARATIVE PHYSIOLOGY. 

An animal must be regarded as a mechanism, but our 
knowledge of a machine is not complete when we know 
its structure ; we must also understand the way the differ- 
ent parts perform their work. The study of the st , ucture 
of an animal is the province of anatomy, while that branch 
of science which deals with the action of the various parts 
and the working of the whole is called physiology. 

It is a far more difficult task to ascertain from the speci- 
mens themselves the function of the parts and the way 
that they act, than it is to make out the details of struct- 
ure, and so a general summary is given here. 

Every machine, in order that it may perform work, 
must be supplied with energy, and the animal obtains 
this energy by the slow combustion (oxidation) of food 
or food products, just as the steam-engine gets its energy 

395 



396 GENERAL ZOOLOGY. 

from the rapid combustion of coal. In the case of a steam- 
engine an engineer supplies the fuel, regulates the action 
of the parts, and disposes of the waste. The animal must 
be its own engineer. It must have the means of obtaining 
fuel (food), of putting it in such position that the energy 
produced by its oxidation can be utilized to its fullest 
extent, and all waste can be properly disposed of. This 
has led, in the first place, to the formation of a digestive 
tract, in which the food is put in such shape as to be most 
advantageously used by the organism. 

In the lowest animals (lowest Protozoa) we find that 
the whole body (cell) serves as a digestive tract, and that" 
food can be taken in at any point on the surface. A 
little higher (p. 162) an organ which we must call a mouth 
is formed in the body, and this opening for the taking in 
(ingestion) of food is found in all higher animals, except 
a few parasites which, living on liquid food, need no such 
opening. With larger animals a definite digestive cavity 
or canal is formed, the lining of which has certain definite 
work to perform. Most articles of food are insoluble as 
taken into the body ; a bit of meat or starch can be soaked 
indefinitely in pure water or may even be boiled for days 
without passing into solution. In the digestive tract 
juices are produced which alter these substances so that 
they can be dissolved; and it is only when they are in 
solution that they can pass through the walls of the 
alimentary canal to those parts where they are to be 
utilized. 

In the lower animals all parts of the digestive tract seem 
able to act at once as formers of digestive fluids, and in 
taking up of the dissolved food, but as we pass higher in 
the scale complications of various kinds are introduced. 
In the first place, we find certain organs, like the salivary 



PHYSIOLOGY. 397 

glands, ^ stomach, pancreas, and liver, set apart for the 
secretion of digestive fluids, and even in animals as low 
as the sea-anemone the mesenterial filaments (p. 169) 
appear to have the same power. On the other hand, the 
other portions, while they may secrete, are pre-eminently 
the regions for the absorption of the liquefied food. An- 
other complication is this : A given amount of surface can 
absorb only so much in a given time; so as to obtain the 
necessary amount of food the surface must be increased. 
This explains in part the folding of the wall of the digestive 
tract in the sea-anemone, as well as the lengthening and 
coiling of the intestine in tadpole and rat, and the spiral 
valve in the shark. In many vertebrates the surface is 
still further increased by numerous minute foldings and 
outpushings of the lining of the intestine which, though 
so small as to be invisible to the naked eye, still more than 
double the surface. 

With most food there are certain portions which are 
indigestible. These of course must be eliminated. In 
the Ccelenterates and flatworms the only opening through 
which they can pass out is the same one by which they 
entered, and so this opening, usually called the mouth, 
serves at once as mouth and vent. In the higher forms 
the alimentary canal becomes a complete tube with two 
distinct openings, one — the mouth— for the taking in of 
food, the other — anus or vent — for the ejection of non- 
nutritious portions. 

After its solution the food (nourishment) must be trans- 
ferred to the parts which are to do the work. In the 
Protozoa the same parts which digest do the work. In 
the sea-anemone and flatworms the pouching of the diges- 
tive tract (figs. 17, 24) renders the transfer easy, for the 
pouches extend to all parts. Above these forms we find 



398 GENERAL ZOOLOGY. 

circulatory organs present, one of the functions of which is 
the carrying of the dissolved food from the digestive tract 
to the working parts. These circulatory organs are tubes 
through which the fluid flows, but a flow can only be 
produced by some mechanism which shall propel the 
fluid. In most cases this is effected by muscles in the 
walls of the vessels, which by waves of contraction force 
the fluid along. In the lower worms and even in 
Amphioxus (p. 289) all of the vessels are markedly con- 
tractile and no part has supremacy over another. As 
we go higher in the scale the tendency is constantly 
towards a concentration of these pumping muscles in 
one region, and thus a heart results. 

So far we have traced the fuel to the working parts. 
In order to do work the fuel must be oxidized, and this 
means that oxygen must also be brought to these parts. 
This oxygen is found either in the air or dissolved in the 
water in which the animal lives. In the Coelenterates, 
flatworms, and many other forms, the general surface of 
the body is sufficient for the absorption of the oxygen, 
but where the animal is larger and needs more oxygen 
special provisions are needed. 

A very simple condition, physiologically, is found in the 
insects, where air- tubes (tracheae, p. 239) extend inwards 
from the outside, their fine branches reaching to every 
part of the body. Air is drawn into these tubes by an 
enlargement of the body by suitable muscles, and then, 
when the oxygen is absorbed, contraction forces out the 
remainder. This breathing process can be seen by watch- 
ing the abdomen of a grasshopper or a wasp. So far the 
circulating fluid is largely nutrient in character, as it 
carries only the food (and some of the waste) . 

In many Crustacea, in molluscs, worms, and vertebrates, 



PHYSIOLOGY. 399 

the conditions are more complicated. In these the nutri- 
ent fluid is also the bearer of the oxygen ; and, in order that 
the fluid may obtain this element specialized portions are 
developed, where the circulatory fluid may come into 
close relationship with the water (gills) or the air (lungs). 
In some (see the figure of Doris, p. 200) the gills project 
freely into the water, and there is no need of special appa- 
ratus for changing this fluid. In other forms the gills are 
protected by enclosure in a branchial chamber, and then 
the water containing the oxygen must be brought here. 
In the oyster and clam this is effected by numerous minute 
hair-like structures (cilia) which by their constant motion 
draw water over the gills. The squid gets its supply by 
enlarging and contracting its mantle-cavity, the crayfish 
by pumping water over the gills by means of its 'gill-bailer' 
(p. 69), and the fish and tadpole by taking water into 
the mouth and forcing it out through the gill-slits. The 
lungs of the higher vertebrates possess a resemblance to 
the tracheae of the insects in that air is drawn into them; 
but here the similarity ceases, for in the vertebrates the 
air is brought from the lungs to the working parts by the 
intervention of the nutrient fluid (blood). 

The methods by which air is drawn into the lungs 
vary. The frog swallows the air by aid of the muscles 
extending across the throat between the halves of the 
lower jaw, and that this swallowing is the only way of 
forcing air into the lungs is shown by the fact that if the 
mouth be kept from closing the animal will suffocate.* 
In the Sauropsida the muscles between the ribs and those 
forming the walls of the abdomen are concerned in the 
inspiration and expiration of air; while in mammals the 

* The skin is a very important organ in the respiration of the 
Batrachia (see p. 337). 



400 GENERAL ZOOLOGY. 

muscular partition (diaphragm) which divides the body- 
cavity becomes an efficient organ in the process (see p. 309). 

We naturally think of work in terms of motion, and in 
the case of an animal the contraction of a muscle or the 
movement of a part or the whole of the body naturally 
suggest themselves as examples. These, however, are 
but a part of the work which the animal does. The per- 
formance of any function of the body is really work. 
When a gland secretes, a nerve acts, an intestine absorbs, 
or the mind carries on its operations, the expenditure of 
energy is called for just as in the contraction of a muscle. 
So all parts must have both food and oxygen. 

When coal is burned in an engine, besides energy there 
is a production of waste. A part of this waste passes off 
in a gaseous condition as water vapor and part as ashes. 
When any part of the animal body works there is a similar 
formation of waste, and the carbon dioxide and water 
vapor are carried away by the same structures (trachese 
in the insects, blood-vessels and gills or lungs in many 
other forms) which brought the oxygen to the parts. 

The animal, unlike the engine, needs also for its fuel 
substances known to the chemist as nitrogenous food 
(proteids) and the combustion of this produces, besides 
the carbon dioxide and water, nitrogenous waste, and 
this, in all of the higher animals, is eliminated by means 
of organs which can be grouped under the common name 
of excretory organs. Here are to be placed not only 
those structures specifically called kidneys in the fore- 
going pages, but also the green gland of the crayfish, the 
Malpighian tubes of insects, the nephridia of the earth- 
worm, and the organ of Bo j anus in the clam. Even the 
contractile vacuole of the Protozoa seems to be an organ 
for the excretion of nitrogenous waste. 



PHYSIOLOGY. 401 

We have seen that the fluid propelled by the heart may 
have a large series of different purposes to fulfil. It must 
carry nourishment from the digestive tract to the different 
parts of the body; it has to carry oxygen from the gills 
and lungs to these various structures, and to carry the 
carbon dioxide and water produced by work to the same 
lungs and gills, while the nitrogenous waste must be 
carried to the excretory organs. The fluid which does all 
this is the blood. 

It is further to be noted that the flow of the blood, un- 
like that of the air in the tracheae of insects or the lungs 
of vertebrates, is not tidal, but forms a complete circula- 
tion, entering the heart by different vessels and different 
openings than those by which it leaves that organ. 

There are other aspects of animal physiology to be re- 
viewed. The animal needs to be aware of the presence of 
food and of the proximity of things injurious to it. This 
implies the formation of a sensory system, and naturally 
this system must be on the outside of the body, for from 
without come both food and danger. The knowledge of the 
presence of good or of evil would be of little value to the 
animal were it without ability to avail itself of this knowl- 
edge. Hence this sensory system is connected with a 
nervous system, which directs and controls the actions of 
the animal. In the lower animals most parts of this 
nervous system are on the surface, but as this superficial 
position is dangerous to such an important structure, we 
find in all the higher animals that the nerve centres or 
ganglia become removed to a deeper position, which 
necessitates the development of nerve-cords to connect 
them with the sensory system and with the muscles and 
other parts. It is interesting that in all animals, even in 
man, no matter how deeply situated or how thoroughly 



402 GENERAL ZOOLOGY. 

protected it may be in the adult, the central nervous 
system arises from the outer surface (ectoderm, p. 155) and 
secondarily attains its permanent position. 

Since most animals must search for their food, we find 
that except in the lower forms, one end becomes adapted 
for always going in front, and in this way a head has come 
into existence, and here are situated the brain and the 
most important sensory organs, as well as the mouth, 
since this part of the body first comes into the neighborhood 
of substances useful as food or likely to be injurious to the 
animal. Further, it is probable that this same loco- 
motion has resulted in bilaterality of the body, which is so 
marked in all animals except the Ccelenterata and sponges. 

Locomotion implies motion of the parts, and when 
resolved to its ultimate all motion is to be referred back 
to the contractility of protoplasm (p. 139). In the lower 
Protozoa (Amoeba, p. 148) all parts of the protoplasm 
(cell) are equally contractile, but from this point onward 
specialization sets in. In some there occurs the develop- 
ment of special vibratile organs — cilia and flagella — 
moved by contraction of the protoplasm in them or at 
their bases. Cilia and flagella occur in most groups 
where a slow motion is needed. Cilia occurs even in 
man in the trachea, and doubtfully in the tubules of the 
kidney, while the tail of the spermatozoan is but a flagellum. 
Another type of modification is the conversion of a part 
of the protoplasm of the cell into muscular substance 
which contracts under stimulus. Traces of this appear 
even in the Protozoa (Stentor, p. 146), and it is abundant 
in all other groups except sponges. Cilia are apparently 
automatic in action and while in a few instances they may 
be regulated by something like nerves, they are not stimu- 
lated by them. Muscles, however, are quiescent unless 



MORPHOLOGY. 403 

stimulated, and this stimulation is usually and normally 
effected (how is not known) by nervous impulse. 

Another physiological peculiarity which needs mention 
is the power of the cells to take only those substances 
which they need from the circulating fluids and to build 
them up into compounds for use in the cell itself, as in the 
case of muscle- and nerve-cells, for use in other parts of 
the organism, as in the case of the liver and pancreatic cells 
or for elimination from the body (kidneys, sweat glands, 
etc.). 

So far we have treated of the animal as an automatic 
self -regulating machine, but in one respect it differs from 
all machines of human production. No amount of fuel 
put under the boiler of a steam-engine will cause this 
mechanism to increase in size or to give rise to other 
bits of mechanism like itself. The animal machine grows 
by the taking in of food, and like the steam-engine, it 
wears out. It, however, has the power of reproducing 
the kind, by the formation of small parts (either buds 
or eggs), which eventually grow into animals like the 
parent which produced them, and thus the species is 
perpetuated, the young taking the place of the generation 
which has worn itself out. 



GENERAL MORPHOLOGY. 

We are now in position to review some of the facts 
already discovered in the laboratory or described in the 
accompanying text, to add to them, and to draw some 
general conclusions. 

Excepting sponges and some Protozoa, each and every 
animal can be placed under one of two heads. In the 



404 GENERAL ZOOLOGY. 

one, the body is bilaterally symmetrical. In it we can 
recognize anterior and posterior; dorsal and ventral; 
light and left. Under the other we place those forms in 
which these features do not exist; there is no right and 
left, but the parts are radially arranged around an axis, 
like the spokes around the axle of a wheel. To this latter 
group belong the coelenterates ; to the first, all other 
divisions reviewed in this volume. Even the Echino- 
derms belong to the bilateral type, for their development 
(fig. 90) shows that in the early stages they have not a 
trace of radial symmetry, but only acquire it later in 
life. 

In the bilateral animals, in turn, two types can be 
recognized: the segmented and the unsegmented. The 
segmented forms show their peculiarities in the most 
striking manner in some of the Annelids, like the earth- 
worm. In these the body is made up of a series of rings 
or segments, each essentially like its fellow, and each 
containing a portion of all systems of organs — muscular, 
nervous, circulatory, digestive, excretory, etc. In the 
arthropods this segmentation again appears, but here 
there are tendencies in two directions: towards a fusion 
of segments, and towards an increase of one segment at 
the expense of another. In annelids and arthropods this 
segmentation is visible externally; in the vertebrates it 
is not so plainly shown, but it nevertheless exists. The 
trunk muscles (see p. 17) are thus arranged; the spinal 
nerves and the vertebrae correspond to the muscle seg- 
ments, as do also certain blood-vessels (intercostals), 
while in their early history the kidneys are segmentally 
arranged. 

On the other hand, the lower worms show no traces of 
segmentation, while the molluscs show it to a very slight 



MORPHOLOGY. 405 

extent.* In the echinoderms there is a repetition of 
ambulacra and ambulacral plates, but this is supposed 
to be different in its origin from that in the segmented 
animals. 

Study of different animals further reveals the fact that 
in some there is no cavity inside the body aside from that 
of the digestive tract (sponges, ccelenterates), while in all 
others there are more or less well-marked cavities between 
the alimentary canal and the body-wall. Further and 
more detailed studies lead to the conclusion that there 
may be at least three different categories of cavities in 
the body, those of the excretory organs, those of the circu- 
latory organs, and a third, the coelom, sometimes small 
and containing only the reproductive glands, sometimes 
large, as in the vertebrates, and including not only the 
reproductive organs, but other structures as well. So the 
term ' body-cavity,' often used, is inexact. The body- 
cavity of a lobster, for example, is merely an expansion of 
the circulatory system and has no relation to the body- 
cavity of the fish or frog, which is a true ccelom. Thus 
the large cavity of the echinoderm and that of the am- 
bulacral system, the pericardium of the mollusc, the 
paired 'body -cavities' of the annelids, the cavities of the 
reproductive organs of the arthropods, and the pleuro- 
peritoneal and pericardial cavities of vertebrates are all 
cceloms. 

All animals reproduce sexually, as mentioned on p. 141, 
but besides this sexual reproduction, many animals pos- 
sess the power of reproducing asexually. In these cases 
the animal may divide into two (fission), or a small por- 

* The gills, kidneys, and heart of the Chitons (p. 197) and the 
Nautilus (p. 211) are supposed to present indications of segmenta- 
tion. 



406 GENERAL ZOOLOGY. 

tion may protrude as a bud which will eventually produce 
an individual more or less like the parent {gemmation). 
This asexual reproduction is very common among the 
Ccelenterates, but it may also occur among the lower 
worms (p. 179), the Polyzoa, the tunicates, etc. 

In many instances this asexual reproduction does not 
result in the formation of distinct and separate animals, 
but buds and parents may remain somewhat intimately 
connected with each other, the result being the formation 
of what are known as colonies, of which Pennaria may be 
taken as a type. Here we are met with a difficulty in 
the use of terms. We have spoken heretofore of in- 
dividuals; but is each hydranth in a colony of Pennaria 
an individual, or is the colony itself to be so regarded, the 
hydranths being regarded as organs? 

In many cases this reproduction by budding results in 
the formation of parts very different from each other. 
Thus in the hydroid (fig. 175) abundant on shells in- 
habited by hermit-crabs, the colony consists of three 
different kinds of hydranths: (1) the feeding hydranths (/) 
which take nourishment for the whole colony; (2) the 
protective hydranths (p) which lack mouths, but which 
are richly provided with nettle-cells; and (3) the repro- 
ductive hydranths (r), the sole function of which is the 
reproduction of the species. In the Siphonophores this 
differentiation is carried still farther (p. 168), for here 
seven different forms may be developed, and here we 
notice a marked fact in colonial conditions. The more 
different the members of the colony become the more it 
conveys the impression of being a single animal instead of 
an aggregate. 

When there are but two different forms in the history 
of the species it is called dimorphic (from the Greek mean- 



MORPHOLOGY. 



407 



ing two forms) ; if more than two, the species is polymor- 
phic, no matter whether the forms are colonial or whether 
they lead distinct lives. 
Besides the di- or polymorphism produced by budding, 




Fig. 175. — Part of a colony of the hydroid, Hydractinia, an illustration of poly- 
morphism. /, feeding individuals; p, protective individuals; r, reproduc- 
tive individual. 



similar conditions may arise in other ways. Thus fre- 
quently we find sexual dimorphism, in which the male and 
female of the same species are greatly different in their 
appearance. An example of this is familiar in the can- 
kerworm-moths, the male of which is winged, the female 
wingless. More striking cases are furnished by many 
Crustacea where the female has become so aberrant that 
in the adult all arthropod features may have disappeared 
(fig. 176). 



408 



GENERAL ZOOLOGY. 




Fig. 176.— Male (to) and female (/) 
of one of the isopod Crustacea, an 
extreme example of sexual di- 
morphism. 



Again, we have to recognize a seasonal dimorphism. Thus 

certain butterflies produce 
several broods in a year. 
Those of the summer broods 
are so different from those 
which come from cocoons 
which have passed through 
the winter, that without 
following through the whole 
history the relationships 
would not be suspected. 
Closely connected with this polymorphism is the phe- 
nomenon of alternation of generations, of which instances 
are abundant in some groups of the animal kingdom 
(p. 167). Thus in the butterflies just mentioned, from 
the eggs of the winter-brood individuals are produced 
(the summer brood), presenting far different appearances 
from the parents, while the eggs of the summer brood 
produce in turn the winter brood. Again, in certain 
gall-wasps the difference between two generations is so 
great — both in appearance and in habits — that they 
would never be regarded as belonging to the same species, 
or even to the same genus, were it not that the whole his- 
tory had been followed, so that it was ascertained that 
each generation resembles, not its parents, but its grand- 
parents. Another and a more complicated example is 
furnished by the liver-fluke (p. 180). 

Many animals in the course of their development pass 
through a metamorphosis, which is not to be confused with 
polymorphism. In forms where a metamorphosis occurs 
the young (the larva), as it hatches from the egg, is greatly 
different from the parent, but by successive changes of 
form it at last reaches the adult condition in which it 



DISTRIBUTION 409 

resembles closely the parent. These metamorphoses at 
times give us clues as to the past history of the group. 
Thus the larvse of Echinoderms (p. 273) and the tadpoles 
of the Anura (p. 337) point to the fact that the first group 
has descended from markedly bilateral ancestors, and that 
the radiate condition of the adult has been secondarily 
acquired; while the history of the frog is evidence that 
these amphibians have sprung from tailed water-breathing 
ancestors. In the insects, on the other hand, the larval 
and pupal stages have far less significance, but have 
apparently been introduced into the history the better to 
adapt these forms to the various conditions of their exist- 
ence (p. 242). 

GEOGRAPHICAL DISTRIBUTION. 

The most superficial observation shows that the differ- 
ent regions of the earth are inhabited by different animals, 
and the same, though not so evident, is true of the sea. 
The animals found in a given region constitute its fauna, 
and the study of these faunae and the causes underlying 
them is one of the most interesting branches of zoology. 

From detailed studies of the distribution of the higher 
vertebrates most zoologists have come to recognize six 
primary land regions : (1) ThePalaearctic, including Europe 
and the southern shore of the Mediterranean, and Asia 
south to the Himalayas; (2) the Ethiopian, including 
Africa south of the Sahara; (3) the Oriental, including 
southern Asia and the islands as far east as Celebes, (4) 
the Nearctic, embracing North America south to about 
the Mexican boundary; (5) the Neotropical, consisting 
of the rest of the American continent; and (6) the Aus- 
tralian, composed of Australia, the islands of the Pacific, 



410 



GENERAL ZOOLOGY. 



and the eastern Malay archipelago. These regions are 
not all equivalent. The Australian is most markedly 
separated from the rest, while the Nearctic and the Palm- 
are tic are closely similar; indeed, are often united as a 
Holarctic region. 

The Australian region is characterized by the mono- 
tremes and by the great abundance of the Marsupials, 




Fig. 177. — Main geographical regions of the earth. Horizontal lines Pala3- 
arctic; vertical lines, Nearctic; coarse oblique, Ethiopian; fine oblique, 
Neotropical; cross-lined, Oriental; dotted, Australian. 

forms which occur nowhere else, except a few species in 
America. The absence of all other mammals, except 
those which might have drifted there or have accom- 
panied man, is noticeable. 

The Neotropical region contains the platyrrhine apes, 
numerous rodents and edentates, and has an almost entire 
absence of insectivores. The llamas and alpacas are 
noticeable, while numerous families of birds, among them 
the humming-birds and the toucans, are characteristic. 

The Ethiopian region is marked by the presence of the 



DISTRIBUTION. 411 

hippopotamus and giraffes, the numerous Antilopes, and 
the gorilla and chimpanzee, while a part of it — Madagascar, 
often set off as a Malagassy region — is the great home of 
the lemurs. 

The lemurs, elephants, and rhinoceroses, which also 
occur in Africa, are found in the Oriental region, which 
has besides the orang-utan and the gibbons. The mon- 
keys of this and the Ethiopian region belong to the 
Catarrhine division. 

The Palmare tic region abuts against the Oriental, Ethi- 
opian, and Nearctic regions, and members of each extend 
into it so that it is not so sharply marked as the rest. 
Indeed, it is characterized more by what it lacks than by 
what it contains. Among the more striking members of 
the fauna are the chamois, the horses, and the great num- 
ber of deer. 

The Nearctic region is characterized by the presence of 
the pronghorn antelope, the sewellel, the star-nose mole, 
and Rocky Mountain goat, as well as by the great num- 
bers of tailed amphibians and ganoids. It is capable of 
subdivision into an Arctic region, essentially similar to 
that of the Palsearctic, an eastern region, including most 
of the United States east of the Rocky Mountains, a 
Pacific region, and a Sonoran region, which merges into the 
Neotropical of Mexico. 

In the oceans similar divisions may be made, but only 
a few of the broader features need mention here. The 
Arctic, the temperate, and the tropical seas each have 
their peculiar and characteristic faunae, the temperate and 
tropical regions being subdivided by the continents into 
Pacific and Atlantic areas. Again there is an eastern 
and a western Atlantic and similar Pacific areas. The 
boundaries between these are less marked than in the 



412 GENERAL ZOOLOGY. 

regions on land, but on our Atlantic coast we can set the 
boundaries at approximately Cape Cod and Cape Hat- 
teras; the Arctic fauna extending down to the former; 
the tropical, though not so distinctly, up to the latter 
promontory. Besides these coast areas there exists a 
pelagic fauna composed of animals which live on the 
surface of the high seas, and another abyssal fauna con- 
taining those in the greater depths (500 fathoms and 
more) of the sea. 

These different faunae suggest numerous problems, only 
one or two of which can be alluded to here. In part the 
differences between them are easily explicable upon 
climatic grounds, but there are numerous others which 
are not solved so easily. Why are the Marsupials re- 
stricted to America and the Australian region? Why 
are all the ostrich-like birds, except the ostrich itself, 
confined to the southern hemisphere? How is the pe- 
culiar distribution of the Dipnoan fishes (p. 334) to be 
explained? Clearly these are not the result of climate. 
Not all these questions have been answered, but the solu- 
tion of many is found in the study of the past history of 
the earth when it is found that once North America and 
the Old World were connected and that once Marsupials, 
for instance, occurred in Europe as well. A knowledge 
of this past history shows that the later the connection 
between two regions of like climatic conditions the more 
close their faunae are related to each other, while those 
which have been separated for a greater length of time 
are much more distinct, for their inhabitants have had 
a longer opportunity to develop in their own lines. 



DISTRIBUTION. 413 



GEOLOGICAL DISTRIBUTION. 

Geographical distribution treats of the distribution of 
animals in space; there is also a distribution in time. 
The animals of past ages have left their record in the rocks, 
and a study of these fossils shows that in the past the ani- 
mals in any region were more or less different from those 
in the same region to-day. Thus at the time of its dis- 
covery America contained no elephants, camels, horses, 
or rhinoceroses, yet the rocks of our western states have 
revealed the skeletons of all of these animals. 

Geologists have classified the rocks according to their 
age, and by studying the fossils which they contain we 
get not only an idea of the changes in a region, but also 
of the progress of life on the earth as a whole. Going 
from the older to the newer rocks the following are the 
main subdivisions of time recognized by geologists and 
the characteristic animals contained in each. 

I. Azoic or Archaean Age. 
No fossils are certainly known from this age. 

II. Paleozoic Age. 

Divided into (1) Cambrian, (2) Silurian, (3) Devonian, 
(4) Carboniferous, and (5) Permian periods. In the 
Cambrian rocks only invertebrates occur: Brachiopoda, 
trilobites, molluscs, and echinoderms prev&iL Corals and 
fishes appear in the Silurian, amphibia in the Carbonifer- 
ous, reptiles in the Permian. 



414 GENERAL ZOOLOGY. 

III. Mesozoic Age. 

Divided into (1) Triassic, (2) Jurassic, and (3) Cretaceous 
periods. This was the age of reptiles, the group reaching 
its culmination in the Cretaceous, some of the species being 
of gigantic size. The mammals appear in the Triassic, 
but they are few in number and are rare in the other 
Mesozoic rocks. The earliest known birds are in the 
Jurassic. 

IV. Cenozoic Age. 

Divided into (1) Eocene, (2) Miocene, (3) Pliocene, (4) 
Pleistocene, and (5) Recent periods. The first three periods 
are grouped as the Tertiary the other two as the Quaternary 
divisions. The Caenozoic is pre-eminently the age of 
mammals. 



EVOLUTION. 

It was long thought that the million or more different 
species of animals on the earth (and the same is true of 
plants) were specially created and placed in conditions 
best adapted for them, but with deeper knowledge this 
view has now become obsolete. At the beginning of the 
last century (1809) Lamarck advanced the view that the 
living species had come into being by modification of 
pre-existing forms. The time was not ready for this 
view; the facts had not been accumulated to support it 
and so it was forgotten, until, in 1859, Darwin published 
his " Origin of Species," which put the theory of evolution 
upon a firm basis, and which since that time has influenced 
almost every line of human thought, and has been accepted 
by every zoologist, in its broader features, although there 



EVOLUTION. 415 

are details which are still in dispute. Some of the factors 
may be outlined here. 

Fertility and the Struggle for Existence. — Animals tend to 
multiply in a geometrical ratio, the number of individuals 
in any generation being the number in the preceding 
multiplied by the number of young produced. This 
rapidly results in enormous numbers. Thus Darwin has 
estimated that the progeny of a single pair of elephants, the 
slowest breeders among animals, would number 19,000,000 
in about 750 years. In other animals the rate is far more 
rapid. The dogfish (Acanthias) breeds at the age of two 
years and produces, on the average, six young at a birth. 
The English sparrow breeds four times a year, laying six 
eggs in a clutch. The full-grown codfish produces over 
a million eggs a year. With many lower animals the rate 
of increase is even greater. Maupas states that if the 
Protozoan he studied were to continue to reproduce at 
its most rapid rate, the result, in thirty-eight days, would 
be a mass of Protozoa equalling the sun in size. 

We know, however, that there is no such actual increase 
in the number of individuals. In fact, from year to 
year the number of any species varies but little. In 
other words, the great majority of eggs or young pro- 
duced fail to come to maturity, but die at an early age. 
Only a small minority survives. There is constantly a 
struggle for existence with every species, and it is evident 
that, in the long run, only those best fitted for their sur- 
roundings will survive, while those less fit will perish. 
In fact, even a very slight difference may determine the 
fate of the individual. This struggle may be between 
(1) individuals of the same species; (2) between different 
species which prey upon or serve as food for each other; 



416 GENERAL ZOOLOGY. 

or (3) between the individual and its environment. In 
what way is difference in fitness brought about? 

Variation. — Animals and plants are continually vary- 
ing. Children of the same parents differ from their 
father and mother and from each other in size, features, 
color of eyes and hair, as well as in mental characteristics. 
The differences may be slight, but still they are notice- 
able. So, too, the chickens of a brood, the kittens of a 
litter, the caterpillars from an egg cluster are not exact 
repetitions of one another, but each has its own indi- 
viduality. The same is true of every animal and every 
plant. 

These variations between the individuals of a species 
would naturally be in different directions. Some individ- 
uals would differ from the rest in such a way as to fit 
them better for their surroundings. They might have; 
keener senses or quicker motions and thus be better 
adapted to obtain their food or to escape their enemies,. 
On the other hand others might vary in such a way as 
to be handicapped in the struggle for existence. In such 
a severe contest as is going on, where only a small fraction 
of a generation can survive, any advantage, however slight, 
may decide the question of life or death. It logically 
follows that in the long run only those whose variations 
have been in a beneficial direction will arrive at maturity, 
and that only those which have thus varied to some ex- 
tent, however slight, from their ancestors, will produce the 
next generation. 

There may be two kinds of variation. In the first the 
modifications from the ancestor may arise from the 
germ-cells (eggs and spermatozoa) and be in no way de- 
pendent upon external conditions. Thus the markings 
of a litter of kittens, the differences between twins, are 



EVOLUTION. 417 

readily seen to be independent of any variation in con- 
ditions and can only be explained by differences in the 
germ-cells from which they arise. Such modifications are 
called congenital variations. The second, or so-called 
acquired variations, depend upon external conditions. 
Two plants from the same lot of seeds will present con- 
siderable differences provided one be well fed while the 
other is placed in soil deficient in nutrition. So, too, use 
and disuse of parts, differences of temperature, of moist- 
ure, etc., will produce variations. 

Another and an important factor is heredity. Certain of 
these variations will be inherited. The congenital varia- 
tions certainly are; there is a question as to the trans- 
missibility of those which are called acquired. Now, 
with constant variations in different directions, the con- 
stant elimination of the unfit, and the inheritance of 
those variations which have been of benefit, the appear- 
ance of the species will gradually change; and since 
different kinds of beneficial variation may occur, the result 
will be to split the originally homogeneous species into 
races. A continuation of the process will produce such 
divergences that the resulting forms must be regarded 
as distinct species, genera, and higher groups. 

The process is aided by other factors. If the varying 
forms be in such position that they can interbreed, there 
will be a constant tendency towards the disappearance of 
the variation. But if they be isolated, the chances of a 
favorable variation being perpetuated will be greatly 
increased. Such isolation is brought about when birds, 
blown out to sea, have colonized a distant island, or where, 
as has frequently happened, the sea divides an area of 
land inhabited by a species into two distinct tracts. 

As a rule this evolution is progressive the new forms 



418 GENERAL ZOOLOGY. 

are higher and more differentiated than their ancestors, 
but occasionally — and usually the result of parasitism — 
degeneration occurs and organs not needed for the para- 
sitic life gradually disappear. Almost all phases of this 
can be seen in the parasitic Crustacea (p. 222) from forms 
where the degeneration has just begun to those in which, 
in the adult female, every crustacean feature has disap- 
peared and the position of the species in the class is only 
recognized from the young. In the cestode worms (p. 181) 
degeneration has gone even further and the ancestral 
features have been lost from the development. 

Carrying these ideas of evolution to their logical con- 
clusion, it follows that all the millions of species now on 
the earth, or which have lived on it in the past, have 
arisen from a few original forms, and that these ancestors 
must have been very primitive in their structure. The 
farther back the divergence between two forms took 
place the wider are the groups apart, while those more 
closely allied must have separated in more recent times. 
It also follows that our systems of classification should aim 
to express the lines and degrees of blood-relationship, like 
a genealogical tree. A third conclusion is that the totality 
of organization is an adaptation to the surroundings, and 
hence not infrequently similarities between two species 
in certain matters of detail are to be explained, not as 
inheritances from a common ancestor, but as having 
arisen independently in response to external conditions. 

The theory of evolution explains many things otherwise 
inexplicable. It tells us why there has been a regular 
succession of animals in the past, as revealed to us in the 
rocks, where we find a gradual progress from the simple 
to the complex. It explains the peculiarities of geo- 
graphical distribution when taken in connection with 



EVOLUTION. 419 

what we know of the past and present relations of land 
and sea areas. It gives a meaning to many of the facts 
of embryology, such as the occurrence in the young of the 
human being of branchial arteries similar in number and 
relations to those of the fish, the larger part of which 
disappear in the adult. In short, evolution gives to 
biological study and to our conceptions of nature a depth 
which nothing else can supply. 



INDEX. 



Abalone, 199 

Abdomen of arthropods, 217 

Abducens nerve, 300 

Aboral, 110, 276 

Abyssal fauna, 412 

Acanthias, dissection of, 15 

Acanthoderus, 245 

Acanthopteri, 331 

Acarina, 234 

Accessorius nerve, 300 

Acephala, 202 

Acerata, 231 

Acetabulum, 38 

Acipenser, 326 

Acmaea, 199 

Acorn barnacle, 224 

Acquired variations, 417 

Actinozoa, 171 

Adambulacral areas, 275 

Adam's apple, 309 

Adductor muscles, 99 

Adrenal gland, 34 

Afferent arteries, 18, 27, 311 

Afferent nerves, 298 

Aglossa, 341 

Air-bladder, 26, 310, 320 

Air-sacs, 50, 351 

Ala spuria, 49 

Albatross, 358 

Alcohol, 5 

Alligators, 349 

Alpaca, 385 

Alternation of generations, 167, 

408 
Altrices, 352 
Alum cochineal, 9 



Alytes, 341 

Ambergris, 379 

Ambulacra, 110, 274 

Ambulacra! areas, 113, 115, 275 

Ambulacral groove, 113 

Ambulacral plates, 113 

Ambulacral pores, 113 

Ambulacral system, 274 

Ametabola, 241 

Ammonites, 211 

Amoeba, 148 

Amoeba, study of, 132 

Amphibia, 336 

Amphiccelous, 27, 292 

Amphioxus, 289 

Amphineura, 197 

Amphipoda, 230 

Amphitrite, 186 

Ampullae, 111, 117, 275 

Ampullae of sponge, 130, 159 

Anacanthini, 329 

Anaconda, 347 

Anal area, 116 

Anal cercus, 77 

Anal fin, 16, 23 

Anal plates, 116 

Analogy, 144 

Angle-worms, 187 

Angulare, 39 

Animal Kingdom, 137 

Animals and Plants, 137 

Annelida, 183 

Anodonta, 98 

Anolis, 346 

Anomura, 226, 227 

Ant-eaters, 372, 374 

421 



422 



INDEX. 



Antelope, 386 

Antennae, 69, 79, 219 

Antennulae, 69 

Antilocapra, 387 

Ant-lion, 248 

Ants, 255 

Ants, white, 247 

Anura, 341 

Aorta, 18 

Aortic arch, 35, 58 

Apes, 390 

Aphides, 260 

Apoda, 284 

Aptenodytes, 358 

Apus, 222 

Aqueous humor, 304 

Arachnida, 232 

Araneida, 233 

Arbacia, 115 

Arbor vitae, 62 

Archaean age, 413 

Archaeopteryx, 355 

Arch, aortic, 35 

Arch, branchial, 19, 24 

Arch, haemal, 20, 27 

Arch, hyoid, 19 

Arch, neural, 20 

Arch, pelvic, 37 

Arctic region, 411 

Argynnis, 266 

Aristotle's lantern, 117, 281 

Armadillos, 372 

Armv-worm, 262 

Arterial blood, 321 

Arterial bulb, 26 

Arterial trunk, 311 

Arthrobranchiae, 69 

Arthropoda, 215 

Artiodactyla, 383, 385 

Ascon, 158 

Asexual reproduction, 405 

Asiphonida, 204 

Asses, 384 

Assimilation, 139, 396 

Asterias, 110 

Asteroidea, 276 

Atlas, 38, 365 

Atrium, 309 

Atrophy, 70, 215 



Auditory nerve, 21 

Auks, 358 

Aurelia, 174 

Auricle, 18, 26, 59, 310 

Australian region, 409, 410 

Aves, 350 

Axial skeleton, 290 

Azoic age, 413 

Baboon, 391 
Back-bone, 290 
Bacon-beetle, 251 
Balancers, 237, 267 
Baleen, 380 
Barnacles, 224 
Basilisk, 345 
Basiopod, 67 
Basket-fish, 279 
Bath-sponge, 130 
Bats, 376 
Beach-flea, 230 
Bean-weevil, 253 
Bears, 388 
Beaver, 376 
Bedbug, 258 
Bee-moth, 264 
Bee, study of, 87 
Bees, 256 
Beetles, 250 
Bicuspids, 367 
Bilateral symmetry, 404 
Bile-duct, 56 
Biloculina, 148 
Bird, dissection of, 48 
Birds, 350 

Birds of Paradise, 363 
Bison, 386 
Blackfish, 379 
Black-snake, 347 
Blindfish, 328 
Blindworms, 340 
Blister-beetle, 253 
Blood, 314 
Blood-corpuscles, 35 
Blow-fly, 268 
Bluefish, 331 
Boa, 347 

Body-cavity, 17, 25, 405 
Body-layers, 154 



INDEX. 



423 



Bo j anus, organ of, 100, 204 
Bombycid moths, 265 
Bony-fish, dissection of, 22 
Bony fishes, 326 
Borax carmine, 9 
Bot-fly, 268 
Bowfm, 326 
Brachial plexus, 63 
Brachiocephalic artery, 58 
Brachiopoda, 190 
Brachyura 226, 228 
Brain of vertebrates, 298 
Branchiae of lobster, 69 
Branchiae of molluscs, 194 
Branchiee of starfish, 111 
Branchial apparatus, 24 
Branchial arch, 19, 24 
Branchial arteries, 18, 311 
Branchial chamber, 194 
Branchial clefts, 16 
Branchial heart, 105, 195 
Branchial tree, 112, 277 
Branchiostegal membrane, 24 
Branchiostegal rays, 24 
Branchipus, 221, 222 
Bristletails, 243 
Brittle-stars, 278 
Brood-pouch, 73 
Bruchus, 253 
Bryozoa, 189 
Buccal mass, 106 
Budding, 406 
Buffalo, 386 
Buffalo-bug, 251 
Bufonidae, 341 
Bugs, 257 
Bulbus, 311, 321 
Buthus, 232 
Butterflies, 261, 265 
Butterfly, study of, 90 
Buzzards, 360 
Byssus, 206 

Cabbage butterflies, 266 
Caddis-fly, 248 
Csecilia, 340 
Caecum of rat, 54 
Csenozoic age, 414 
Calcarea, 160 



Calcareous sponge, 130 

Calyx, 279 

Cambrian period, 413 

Camel, 386 

Cancer, 229 

Canine teeth, 367 

Canker-worms, 264 

Cannon-bone, 384 

Capillaries, 310 

Capybara, 375 

Carapax, 44, 69, 218, 318 

Carboniferous period, 413 

Cardiac part of stomach of 

starfish, 276 
Carina, 354 
Carmine, 261 
Carnivora, 387 
Carotid artery, 19, 59 
Carp, 328 
Carpals, 297 
Carpus, 38 
Carrion-beetles, 251 
Case-fly, 248 
Cassowary, 356 
Caterpillar, 261 
Caterpillar-hunters, 251 
Catfishes, 327 
Cats, 388 
Cattle, 386 

Caudal fin, 16, 23, 318 
Caudal region, 292 
Caviare, 326 
Cecropia-moth, 265 
Cell organs, 145 
Cells, 140, 156 
Centipedes, 235 
Centrosome, 141 
Centrum, 27, 291 
Cephalopoda, 208 
Cephalothorax, 67 
Cercaria, 180 
Cerebellum, 20, 28, 299 
Cerebral ganglia, 100 
Cerebral hemispheres, 28 
Cerebrum, 20, 28, 299 
Cervical region, 292 
Cervical suture, 70 
Cestoda, 181 
Cetacea, 378 



424 



INDEX. 



Chsetse, 92, 185 
Chsetopoda, 185 
Chameleon, 346 
Chelae, 68 
Chilomonas, 150 
Chilomycterus, 333 
Chilopoda, 235 
Chimsera, 325 
Chimpanzee, 392 
Chinch-bug, 258 
Chinchilla, 375 
Chiroptera, 376 
Chiton, 197 
Chloragogue organ, 94 
Chordata, 286 
C horoid, 304 

Chromatophores, 103, 209 
Chrysalis, 262 
Cicada, 259 
Cilia, 134, 145, 149 
Circulation, 311, 397 
Cirripedia, 224 
Clam, dissection of, 98 
Clams, 207 
Clamatores, 361 
Clam-worm, 185 
Class, 143 
Classification, 142 
Clava, 125 
Clavicle, 37, 296 
Clitellum, 92 

Cloaca, 130, 159, 307, 342 
Cloacal chamber, 100, 287 
Clothes-moth, 264 
Clupea, 329 
Clypeastroidea, 281 
Clypeus, 79 
Coati, 388 
Coccidse, 261 
Cochineal, 261 
Cockroaches, 243, 245 
Cod, 329 

Codling-moth, 264 
Coelenterata, 162 
Cceliac axis, 18, 55 
Coelom, 17, 25, 274, 405 
Ccelomic pouches, 183 
Coleoptera, 250 
Colon, 54 



Colonies, 164, 406 
Colorado potato-beetle, 252 
Colors, conventional, 4 
Columbines, 3C0 
Comatula, 279 
Commissures, 71 
Compound eyes, 70, 78, 217 
Condyles, 365 
Cone-shells, 200 
Coney, 382 

Congenital variations, 417 
Conjugation, 142, 150 
Connective tissue, 54 
Contractile vacuole, 133, 146 
Conurus, 361 
Conus, 311,321 
Conventional colors, 4 
Convergent evolution, 418 
Copepoda, 222 
Coracoid, 37, 296 
Coracoid process, 370 
Coral, 172, 173 
Corium, 318 
Cormorants, 358 
Cornea, 107, 304 
Corpora restiformia, 20 
Corpus callosum, 62 
Corpuscles of blood, 314 
Corydalis, 249 
Cowries, 200 
Coypu, 375 
Coxa, 77 
Crabs, 228 
Cranes, 359 
Crangon, 227 
Cranium, 293 
Cranium of fish, 29 
Cranium of frog, 38 
Crayfish, dissection of, 67 
Cretaceous period, 414 
Cricket, study of, 84 
Crickets, 243, 246 
Crinoidea, 279 
Crocodilia, 349 
Crop, 50, 81, 305, 351 
Croton bug, 245 
Crows, 363 
Crustacea, 218 
Ctenoid scale, 23, 318 



INDEX. 



425 



Ctenolabrus, 332 
Ctenophora, 174 
Cuckoos, 360 
Cucumaria, 283 
Cucumber-beetles. 252 
Cunner, 332 
Cuttle-bone, 209 
Cycloid scale, 23, 318 
Cyclops, 223 
Cyclostomata, 315 
Cypris, 224 
Cytology, 140 
Cytopharynx, 134 
Cytostome, 134 
Crystalline.style, 101, 204 

Dactylocalyx, 160 
Daddy-longlegs, 234 
Dasypus, 373 
Day-flies, 247 
Dealers in material, 5 
Decalcifying fluid, 8 
Decapoda, 211, 226 
Deer, 386 
Degeneration, 418 
Dental formula, 368 
Dentary bone, 24, 39 
Dentine, 375 
Derma, 363 
Dermal tooth, 17 
Devil-fish, 324 
Devonian period, 413 
Diaphragm, 56, 309 
Diastole, 134 
Dibranchiata, 211 
Didelphys, 371 
Diencephalon, 299 
Differentiation, 145 
Difflugia, 148 
Digestion, 396 
Digger-wasps, 255 
Digit, 38 
Digitigrade, 388 
Dimorphism, 406 
Dinosaurs, 349 
Diotocardia, 199 
Diplopoda, 235 
Diphy cereal, 318 
Dipnoi, 334 



Diprotodon, 372 
Diptera, 267 
Directives, 122 
Dissecting-pan, 3 
Dissipiments, 93 
Distribution, geographical, 409 
Distribution, geological, 413 
Dobson, 248 
Dodo, 360 
Dog-day locust, 259 
Dogfish, dissection of, 15 
Dogs, 388 
Dolphin, 379 
Doris, 200 
Dormice, 375 
Dorsal aorta, 18 
Dorsal fin, 16, 23 
Doryphora, 241 
Dragon-flies, 246 
Dragon-fly, study of, 86 
Drills, 200 
Duckbill, 369 
Ducks, 358 
Dugong, 380 
Dura mater, 61 

Eagles, 359 

Ear, 69, 302 

Earthworm, dissection of, 92 

Earthworms, 187 

Eastern region, 411 

Echinarachnius, 282 

Echinoderma, 273 

Echinoidea, 280 

Ectoderm, 125, 154 

Ectosarc, 132 

Edentata, 372 

Educabilia, 378 

Eels, 329 

Efferent arteries, 19, 27, 311 

Efferent nerves, 298 

Egg, 126, 141 

Egret, 359 

Elasmobranchii, 322 

Electric-light bugs, 258 

Elephants, 381 

Elytra, 238, 250 

Embiotocidse, 332 

Emeu 356 



426 



INDEX. 



Enamel, 375 

Endopod, 67, 219 

Endosarc, 132 

Energy, source of, 395 

English sparrow, 363 

Entoderm, 125, 154 

Entomostraca, 222 

Entosarc, 132 

Eocene period, 414 

Epeira, 233 

Epicranium, 78 

Epidermis, 318 

Epiglottis, 60 

Epencephalon, 299 

Ermine, 388 

Errantia, 185 

Ethiopian region, 409, 410 

Eupagurus, 228 

Eustachian tube, 33, 303 

Eutheria, 370 

Euthyneura, 198, 200 

Everyx, 265 

Evolution, 414 

Excretion, 400 

Excretory organs of vertebrates, 

314 
Excurrent canals, 130 
Exoccipital bones, 38 
Exopod, 67, 219 
External meatus, 353 
Exumbrella, 127 
Eye-muscles, 305 
Eyes of arthropods, 217 
Eyes of fish, 23 
Eyes of molluscs, 196 
Eyes of vertebrates, 303 
Eyes, simple and compound, 217 

Face, 293 

Facial nerve, 21, 300 
Fairy shrimp, 221, 222 
False diaphragm, 26 
Family, 143 

Fat body of grasshopper, 80 
Feather tracts, 49, 350 
Feathers, 350 
Feathers, kinds of, 48 
Femur, 38, 77, 297 
Ferrets, 388 



Fertility, 415 

Fertilization, 142 

Fibula, 45, 297 

Fins, 16, 23, 318 

Firefly, 251 

Fishes, 317 

Fish-lice, 222 

Fission, 405 

Fissipedia, 388 

Flagella, 149 

Flagellata, 151 

Flamingo, 359 

Flatfish, 330 

Flatworms, 178 

Flies, 267 

Flipper, 378 

Flounders, 330 

Fluke, liver, 180 

Flukes of whale, 379 

Fly-catchers. 363 

Flying foxes, 378 

Food vacuole, 133 

Foot of mollusc, 193 

Foramen magnum, 38 

Foraminifera, 148 

Formol, 6 

Four-legged butterflies, 266 

Fowl, 357 

Foxes, 388 

Frog, dissection of, 32 

Frogs, 341 

Fronto-parietals, 38 

Furcula, 51, 297, 354 

Gadus, 330 

Gall-bladder of fish, 25 
Gall-bladder of rat, 56 
Gall-flies, 254 
Gallinago, 359 
Gammarus, 230 
Ganglia, 71, 184 
Ganglion, 36 
Ganoid scales, 318 
Ganoidei, 325 
Garpikes, 326 
Gastral cavity, 127 
Gastric artery, 55 
Gastric cseca, 80 
Gastric vein, 55 



INDEX. 



427 



Gastropoda, 197 

Gavials, 349 

Geese, 358 

Gemmation, 406 

Generations, alternation of, 167, 

408 
Genital plates, 116 
Genus, 143 

Geographical distribution, 409 
Geological distribution, 413 
Geometrid moths, 264 
Geophilus, 235 
Gila monster, 345 
Gill-arches, 294 
Gill-bailer, 69 
Gill-bars, 294 

Gill-chamber of lobster, C9 
Gill-clefts, 24 
Gill-cover, 24, 308 
Gill-filaments, 24 
Gill-opening, 24 
Gill-slits, 16, 19, 286 
Gills of lobster, 69 
Gills of molluscs, 194 
Gills of vertebrates, 307 
Girdle, pectoral, 18 
Girdles, 296 
Gizzard, 50, 306, 351 
Glass-snake, 345 
Glenoid fossa, 37 
Globigerina, 148 
Glossopharyngeal nerve, 62, 300 
Glottis, 309 
Glottis of frog, 33 
Glottis of rat, 60 
Glyptodon, 372 
Gnathostomata, 317 
Goats, 387 
Goldfish, 328 
Gonads, 18 
Gonionemus, 127 
Goose-barnacle, 224 
Gophers, 376 
Gorilla, 392 
Grallatores, 359 
Grantia, 130 

Grasshopper, dissection of, 76 
Grasshoppers, 243, 246 
Green gland, 71,218, 220 



Grouse, 357 
Guinea-pigs, 375 
Gullet, 305 
Gulls, 358 

Haddock, 329 
Haemal arch, 20, 27, 291 
Haemal process, 27 
Haemal spine, 27 
Hagfish, 315 
Hair, 363 
Hairworms, 182 
Half-apes, 390 
Halibut, 330 
Haliomma, 149 
Hares, 375 
Harvestmen, 234 
Haustellate, 240 
Hawk-moths, 264 
Hawks, 360 
Hazelnut-weevil, 250 
Head of arthropods, 46 
Head kidneys, 26 
Heart of clam, 99 
Heart of fish, 26 
Heart of grasshopper, 80 
Heart of lobster, 71 
Heart of molluscs, 95 
Heart of rat, 58, 59 
Heart of shark, 18 
Heart-urchins, 282 
Hellgrammites, 248 
Hemimetabola, 241 
Hemiptera, 257 
Hepatic artery, 55 
Hepatic caeca, 111, 277 
Hepatic duct, 112 
Hepatic veins, 57 
Heredity, 417 
Hermit-crabs, 227 
Herons, 359 
Herring, 329 
Hesperornis, 355, 356 
Heterocercal fins, 16, 23, 318 
Heteropoda, 200 
Heteroptera, 258 
Hexacoralla, 173 
Hexapoda, 236 
Hippocampus, 335 



428 



INDEX. 



Hippopotamus, 385 
Hirudinei, 187 
Holocephali, 325 
Holometabola, 241 
Holothuridea, 282 
Homocercal fins, 16, 23, 318 
Homology, 144 
Homoptera, 258 
Hornbills, 361 
Horned pout, 327 
Horned toads, 346 
Hornets, 255 
Horse-mackerel, 331 
Horses, 384 
Horseshoe-crab, 231 
House-fly, 268 
Howlers, 391 
Humerus, 38 
Humming-birds, 362 
Hyenas, 388 
Hydra, 167 
Hydranth, 123, 164 
Hydridse, 167 
Hydrocaulus, 123 
Hydroid, study of, 123, 125 
Hydroid medusa, study of, 127 
Hydromedusse, 167 
Hydrorhiza, 125 
Hydrozoa, 165 
Hylidse, 341 
Hymenoptera, 253 
Hyoid arch, 19 
Hyoid bone, 60, 594 
Hyomandibular, 294 
Hypertrophy, 70, 77, 215 
Hypoglossal nerve, 300 
Hypophysis, 62 
Hyracoidea, 382 
Hyrax, 382 

Ibis, 359 

Ichneumon-flies, 254 
Ichthyopsida, 317 
Ichthyosaurs, 349 
Idotea, 230 
Iliac artery, 56 
Iliac vein, 56 * 
Ilio-lumbar vein, 56 
Ilium, 296 



Imago, 262 
Incisors, 367 
Individual, 406 
Ineducabilia, 378 
Infusoria, 149 
Injecting, 6 
Injection mass, 7 
Ink-sac, 104 
Insecta, 235 
Insectivora, 376 
Insects, classification, 242 
Instruments, 3 
Interambulacral areas, 275 
Interambulacrals, 113, 115 
Intercostal muscles, 309 
Interradial, 110 
Io-moth, 265 
Iris, 107, 304 
Ischium, 296 
Isinglass, 326 
Isopoda, 230 
Isthmus, 24 

Jackals, 388 
Jellyfish, 164, 173 
Jugular veins, 50, 58 
Jumping mice, 376 
June-bug, study of, 85 
June-bugs, 252 
Jurassic period, 414 

Kangaroos, 372 
Kidneys, 314 
Kidneys of dogfish, 18 
Kidneys of fish, 26 
Kidneys of rat, 56, 57 
Kiwi, 356, 
Kogia, 378 

Lab rum, 79 
Lac, 261 
Lacertilia, 345 
Lacunas, 220 
Ladybugs, 251 
Lamellibranchs, 202 
Lampreys, 315 
Lamp-shells, 190 
Lancelet, 289 
Larva, 241, 250, 408 



INDEX. 



429 



Larynx, 60 
Lateral line, 20, 23 
Lateral-line organs, 300 
Layer, supporting, 162 
Layers of body, 154 
Leaf-hoppers, 260 
Leeches, 187 
Lemmings, 375 
Lemurs, 390 
Lens, 107 
Lepas, 224 
Lepidoptera, 261 
Lepidosteus, 326 
Lepisma, 243 
Leptocardii, 289 
Leucania, 262, 263 
Leucocytes, 314 
Lice, 261 
Lice, fish, 222 
Limax, 201 
Limpets, 199 
Limulus, 231 
Lines of growth, 98, 194 
Lingual ribbon, 106, 195 
Lion, 388 
Liver-fluke, 180 
Lizards, 345 
Llama, 385 
Lobosa, 148 

Lobster, dissection of, 67 
Lobsters, 226 
Locomotion, 402 
Locusts, 243, 246 
Long-horn beetles, 252 
Loons, 358 
Lophobranchii, 333 
Luna-moth, 265 
Lung-fishes, 334 
Lung of molluscs, 195 
Lymph hearts, 32 
Lymphatics, 55 

Macaque, 392 
Mackerel, 331 
Macrura, 226 
Madreporite, 110, 274 
Maggots, 267 
Malacostraca, 225 
Malagassy region, 411 



Malaria, 152 

Malpighian tubes, 80, 218, 238 
Mammalia, 363 
Mammals, age of, 414 
Mammoth, 382 
Man, 392 
Manatee, 380 
Mandible of bird, 48 
Mandibles of Crustacea, 219 
Mandible of frog, 38 
Mandibles of insects, 79 
Mandibles of lobster, 69 
Mandibulate, 240 
Mangabey, 392 
Manis, 373 
Mantle, 99, 193 
Mantle artery, 104 
Mantle-chamber, 194 
Manubrium, 127 
Marabou, 359 
Marmosets, 391 
Marsipobranchs, 316 
Marsupial bones, 370 
Marsupialia, 370 
Marten, 388 
Mastodon, 382 
Material, dealers in, 5 
Maxilla of lobster, 69 
Maxillae of Crustacea, 217 
Maxillary bone, 39 
Maxillipeds, 68, 219 
May-flies, 247 
Meckel's cartilage, 40 
Mediastinum, 57 
Medulla oblongata, 20, 29, 299 
Medusa, 164, 173 
Medusa-buds, 124 
Megatherium, 373 
Melicertum, 164 
Menhaden, 329 
Mentomeckelian bone, 39 
Merostomata, 231 
Mesencephalon, 299 
Mesenterial artery, 18, 55 
Mesenterial filaments, 122, 169 
Mesenterial vein, 55 
Mesentery, 17,26, 111, 121, 183, 

307 
Mesoderm, 155 



430 



INDEX, 



Mesoglcea, 126, 162 
Mesonephros, 18 
Mesothorax, 77, 237 
Mesozoic age, 414 
Metacarpals, 297 
Metacarpus, 38 
Metameres, 67, 183, 215 
Metamorphosis, 24, 408 
Metatarsals, 297 
Metathorax, 77, 237 
Metazoa, 154 
Metencephalon, 299 
Metridium, 120, 173 
Mice, 375 
Microstomum, 179 
Midbrain, 299 
Milk dentition, 367 
Milkweed-butterfly, 266 
Mink, 388 
Minnows, 328 
Miocene period, 414 
Mites, 234 
Moccasin, 347 
Mola, 334 
Molars, 367 
Moles, 376 
Molgula, 289 
Mollusca, 193 
Molluscoidea, 189 
Monkeys, 390 
Monotocardia, 200 
Monotremata, 369 
Morphology, 403 
Mosquitos, 269 
Mother of pearl, 206 
Moths, 261 
Motor nerves, 298 
Mourning-cloak, 266 
Mouth-parts of Crustacea, 219 
Mouth-parts of insects, 79 
Mouth-parts of lobster, 68 
Miiller's fluid, 8 
Musca, 269 
Muscle-plates, 17, 25 
Muscle-plates of frogf 33 
Muskalonge, 328 
Muskrat, 376 
Musk-ox, 387 
Mussels, 206 



Mya, 207 

Myelencephalon, 299 
Mylodon, 373 
Myotomes, 17, 25, 33 
Myriapoda, 236 
Myrmeleon, 249 
Mytilus, 206 

Naked molluscs, 200 

Nanda, 356 

Narwal, 379 

Nasal bones, 38 

Natatores, 358 

Nauplius, 221 

Nautilus, 209, 210 

Nearctic region, 409, 411 

Nebalia, 225 

Nemathelminthes, 182 

Neotropical region, 409, 410 

Nephridium, 95, 184, 220, 314 

Nephrostome, 185 

Neptunus, 228 

Nereis, 185 

Nettle-cells, 124, 162 

Neural arch, 20, 291 

Neural process, 27 

Neural spine, 27 

Neuroptera, 248 

Newts, 340 

Nictitating membrane, 44, 48, 

303 
Nidamental gland, 104 
Notochord, 19, 42, 286, 290 
Notochordal sheath, 19 
Nototrema, 341 
Nudibranchs, 200 
Nucleolus, 126 
Nucleus, 126, 133, 140 
Nutria, 375 

Occipital condyle, 38 
Ocelli, 79, 217 
Octocoralla, 172 
Octopoda, 211 
Octopus, 212 
Ocular plates, 116 
Oculomotor nerve, 300 
Odonata, 247 
Odontophore, 136, 195 



INDEX. 



431 



Odontornithes, 356 
CEneis, 267 

(Esophageal commissure, 184 
(Esophagus, 305 
Oil-bottle beetle, 253 
Oil-glands, 350 
Olfactory lobes, 28 
Olfactory membrane, 21 
Olfactory nerve, 20, 299 
Olfactory organs, 301 
Olfactory tract, 20 
Oligochsetse, 187 
Olive-shells, 200 
Olynthus, 158 
Omenta, 17 
Omosternum, 37 
Opercular bones, 29 
Operculum, 24, 198, 308 
Ophidia, 347 
Ophiopholis, 278 
Ophiuroidea, 278 
Opisthobranchia, 200 
Opisthoccelous, 292 
Opossum, 371 
Optic ganglion, 107 
Optic lobes, 20, 28, 299 
Optic nerve, 20, 300 
Optic thalamus, 20 
Oral, 276 
Oral surface, 110 
Orang-utan, 392 
Orbit, 46 
Order, 143 

Organ of Bojanus, 100 
Organ of Corti, 366 
Organs, 154, 156 
Origin of species, 414 
Orioles, 363 
Ornithorhynchus, 369 
Ornithurae, 356 
Orthoceratites, 211 
Ortroptera, 243 
Oscines, 361 
Osculum, 158 
Ossification, 293 
Ostia of heart, 70 
Ostium, 130 
Ostracoda, 224 
Ostriches, 356 



Otoliths, 302 
Otter, 388 
Ovary, 315 
Oviduct, 34 

Ovipositor, 76, 238, 253 
Ox-bot, 268 
Ox-warble, 268 
Oyster, dissection of, 102 
Oysters, 204 

Pachydermata, 384 

Pacific region, 411 

Palsearctic region, 409, 411 

Palate, 60 

Palatine bone, 39 

Paleozoic age, 413 

Pallial line, 101 

Pallial sinus, 101 

Palpi of clam, 99 

Palpus, 79 

Pancreas, 17, 34, 55 

Pangolin, 373, 374 

Panther, 388 

Paper nautilus, 209, 212 

Paramecium, 134, 151 

Parapodia, 185 

Parasita, 261 

Parasphenoid bone, 39 

Parencephalon, 299 

Parieto-splanchnic ganglion, 100 

Parotid gland, 60 

Parrots, 361 

Parthenogenesis, 142 

Passeres, 361 

Pearl-oyster, 205 

Pearls, 206 

Fearly Nautilus, 209 

Pea-weevil, 253 

Pecten, 205 

Pectoral fins, 16, 23 

Pectoral girdle, 18, 296 

Pedal ganglion, 100 

Pedata, 284 

Pelagic fauna, 412 

Pelvic girdle, 38, 296 

Pen, 107 

Pencil, 3 

Penguin, 358 

Pennaria, 123, 165 



432 



INDEX. 



Pentacrinus, 280 

Perch, 332 

Pericardial cavity, 18, 26 

Pericardium, 195, 310 

Perisarc, 123, 165 

Perissodactyla, 383 

Peristome, 115 

Peritoneal cavity, 54, 368 

Peritoneum, 17, 25, 307 

Permanent dentition, 367 

Permian period, 413 

Petromyzon, 316 

Phalangers, 371 

Phalanges, 297 

Phalangida, 234 

Phalangium, 234 

Pharyngognathi, 332 

Pharynx, 24, 305 

Pheasants, 357 

Phyllopoda, 222 

Phylloxera, 260 

Physalia, 168 

Physiology, 395 
Physostomi, 327 
Pickerel, 328 
Picrosulphuric acid, 9 
Pigeons, 360 
Pigs, 385 
Pike, 328 
Pill-bug, 229 
Pinnipedia, 388, 389 
Pinworms, 182 
Pipa, 341 
Pipe-fish, 334 
Pisces, 317 
Pituitary body, 37 
Placenta, 372 
Placentalia, 372 
Placoid scale, 17, 318 
Planaria, 179 
Plantigrade, 388 
Plant-lice, 260 
Plants and animals, 137 
Plasma, 314 
Plasmodium, 151 
Plastron, 44, 348 
Plathelminthes, 178 
Plectognathi, 333 
Pleistocene period, 414 



Plesiosaurs, 349 

Plethodon, 340 

Pleural cavity, 57, 368 

Pleurobranchise, C9 

Plexus of nerves, 36 

Pliocene period, 414 

Ploughshare-bone, 353 

Pneumogastric nerve, 59, 300 

Pocket-rats, 376 

Podobranchise, C9 

Poison-fangs, 347 

Polian vesicles, 113 . 

Polychaetae, 185 

Polymorphism, 407 

Polyphemus-moth, 265 

Polyps, 171 

Polyzoa, 189 

Pompano, 331 

Porcupines, 375 

Porgy, 332 

Porifera, 158 

Porpoise, 379 

Portal vein, 55 

Portuguese man-of-war, 168 

Postcava, 56 
Potato-beetle, 241 
Poulpes, 212 
Prsecoces, 353 
Prairie-dogs, 376 
Prawns, 227 
Precava, 58 

Premaxillary bone, 24, 39 
Premolars, 367 
Preoral lobe, 92 
Primary feathers, 48 
Primates, 390 
Pristis, 323 
Proboscidia, 381 
Proboscis, 123, 127 
Process, haemal, 27 
Process, neural, 27 
Process, transverse, 37 
Proccelous, 292 
Proglottid, 181 
Prometheus-moth, 265 
Prootic bone, 39 
Prosencephalon, 299 
Prothorax, 77, 237 
Protoplasm, 126, 139 



INDEX. 



433 



Protopterus, 335 
Protozoa, 144 
Pro vent riculus, 50, 351 
Pseudoneuroptera, 246 
Pseudopodia, 132, 147 
Pseudopleuronectes, 330 
Pterodactyls, 350 
Pteropods, 201 
Pterygoid bone, 39, 294 
Pterygoquadrate, 294 
Pubis, 296 

Pulmonary artery, 35, 59, 313 
Pulmonary vein, 59 
Pulmonata, 201 
Pupa, 241, 262 
Pupa of beetles, 250 
Pupil, 304 
Pygostyle, .353 
Pyloric cseca, 25, 307 
Pyloric part of stomach of star- 
fish, 276 
Pythons, 347 

Quadrate, 39, 51, 294 
Quadratojugal bone, 39 
Quahog, 203 
Quaternary, 414 

Rabbits, 375 
Raccoon, 388 
Racemose vesicles, 113 
Radial, 110, 113, 127, 174 
Radial nerve, 114 
Radial symmetry, 404 
Radiata, 162, 273 
Radii, 275 
Radiolaria, 149 
Radio-ulna, 38 
Radius, 45, 297 
Radula, 106, 195 
Raia, 323 
Raise, 324 
Ranidse, 341 
Raptores, 359 
Rasores, 357 
Rat, dissection of, 53 
Rats, 375 
Rattlesnake, 347 
Rays of fins, 23 



Recent period, 414 

Rectal gland, 17 

Rectum, 34, 54 

Red coral, 172 

Reference-books, 10 

Regularia, 281 

Remora, 331 

Renal artery, 56 

Renal vein, 56 

Reproduction, 403 

Reproductive organ of dogfish, 

18 
Reproductive organs of fish, 26 
Reproductive organs of frog, 34 
Reptilia, 342 
Reptiles, age of, 414 
Respiration, 398 
Retina, 107, 304 
Retractors, 112 
Rhea, 357 
Rhinoceros, 383 
Rhizopoda, 147 
Rhynchophora, 250 
Ribs, 291 

Ring-canal, 127, 166, 274 
Ring-nerve, 113 
Rodentia, 374 
Roots of nerve, 36 
Rose-beetle, 251 
Round worms, 182 
Ruminants, 385 
Rytina, 380 

Sable, 388 
Sacral region, 292 
Salamanders, 340 
Salivary gland, 60 
Salmo, 328 
Salmon, 328 
Sand-cakes, 281 
Sand-dollars, 281 
Sand-wasp, 256 
Sapajous, 391 
Sauropsida, 342 
Saururse, 355 
Savigny's law, 68, 78, 
Sawfish, 323, 324 
Sawflies, 254 
Scale-bugs, 261 



434 



INDEX. 



Scales of fishes, 23, 317 

Scallops, 205 

Scansores, 360 

Scaphognathite, 69 

Scaphopoda, 201 

Scapula, 37, 296 

Scarabseans, 252 

Sciatic nerve, 36, 63 

Sciatic plexus, 63 

Sclerotic, 304 

Scolex, 181 

Scomber, 332 

Scorpionida, 232 

Scorpions, 232 

Scutellse, 347 

ScyphomedussB, 173 

Scyphozoa, 169 

Sea-anemone, dissection of, 120 

Sea-anemones, 169, 171 

Sea-bass, 332 

Sea-cows, 380 

Sea-cucumbers, 282 

Sea-horse, 334 

Sea-lilies, 279 

Sea-lions, 390 

Sea-peach, 289 

Sea-pear, 289 

Sea-snake, 348 

Sea-squirt, 289 

Sea-urchin, 115, 280 

Seals, 388 

Secondary feathers, 48 

Sedentaria, 185 

Segmented animals, 404 

Segments, 67 

Semicircular canals, 302 

Semilunar fold, 303 

Sensation, 401 

Sensory nerves, 298 

Sepia, 209, 212 

Septa, 93, 121, 169, 183 

Serpent stars, 278 

Setae, 92, 185 

Seventeen-year locust, 259 

Sexual dimorphism, 407 

Sexual reproduction, 405 

Shad, 329 

Sharks, 323 

Sheep, 387 



Sheep-bot, 269 
Sheepshead, 332 
Shell of molluscs, 194 
Shellac, 261 
Shell-gland, 218, 220 
Ship-worm, 207 
Shore-crab, 229 
Shoulder-girdle, 37, 296 
Shrews, 376 
Shrimp, 227 
Silicea, 160 
Silkworms, 265 
Silurian period, 413 
Silver-fish, 243 
Sinus venosus, 18 
Siphon of Acephala, 202 
Siphon of squid, 103, 208 
Siphonal cartilages, 104 
Siphonata, 207 
Siphonoglyphe, 120 
Siphonophore, 164 
Siphons of clam, 99 
Sirenia, 380 
Skate, 323, 324 
Skeleton of frog, 37 
Skeleton of turtle, 45 
Skeletons, making of, 32 
Skippers, 265 
Skull of bird, 51 
Skull of frog, 38 
Skunks, 388 
Sloths, 373 
Slugs, 201 
Smallpox, 152 
Snails, 201 
Snake, study of, 47 
Snakes, 347 
Snipe, 359 
Snout-beetle, 250 
Soft-shell crab, 228 
Somites, 67, 183, 215 
Sonoran region, 411 
Sow-bug, 229 
Sow-bug, study of, 73 
Spanish flies, 253 
Spatangoids, 282 
Specialization, 145 
Species, 143 
Spermaceti, 379 



INDEX. 



435 



Spermatozoa, 126, 141 

Sphenethmoid bone, 38 

Sphex, 256 

Sphinx moths, 264 

Spicules, 130, 159 

Spiders, 233 

Spinal accessory nerve, 62 

Spinal cord, 19, 298 

Spinal nerves, 36, 298 

Spine, haemal, 27 

Spine, neural, 27 

Spinnerets, 233 

Spiny ant-eaters, 369 

Spiracles, 16, 76 

Spiracles of insects, 239 

Spiracular cleft, 308 

Spiral valve, 17, 

Spirostrephon, 236 

Spittle-insects, 260 

Splenic artery, 55 

Splenic vein, 55 

Splint-bones, 384 

Sponge, study of, 130 

Sponges, 158 

Spongia, 130 

Spongida, 158 

Sporozoa, 151 

Spring-beetle, 251 

Spring-tails, 243 

Squali, 323 

Squamosal bone, 39 

Squash-bug, 258 

Squash-bug, study of, 89 

Squid, 212 

Squid, dissection of, 103 

Squirrels, 376 

Stapes, 366 

Starfish, dissection of, 110 

Starfish larva, 273 

Starfishes, 276 

Starling, 363 

Stegocephali, 341 

Stellate ganglia, 210 

Stentor, 151 

Sternum, 37, 293 

Sting of insects, 238, 254 

Stink-bug, 259 

Stolon, 165 

Stomach of vertebrates, 306 



Stomach-worms, 182 
Stone-canal, 112, 274 
Storks, 359 

Streptoneura, 198, 199 
Strombus, 200 
Strongylocentrotus, 115 
Struggle for existence, 415 
Struthii, 356 
Sturgeon, 326 
Stylonichia, 150 
Subclavian artery, 59 
Subclavian vein, 58 
Subumbrella, 127 
Suckfish, 331 
Sunfish, 332, 333 
Supporting .layer, 126, 162 
Supra-anal plate, 77 
Supra-renal capsule, 56 
Supra-scapula, 37 
Surf-fish, 332 
Surinam toad, 341 
Survival of fittest, 415 
Suspensory apparatus, 322 
Swallowtail-butterflies, 266 
Swans, 358 
Sweetbread, 310 
Swellfish, 333 
Swim-bladder, 310, 320 
Swimmerets, 67 
Swine, 385 
Sword-fish, 331 
Sycon, 159 
Symmetry, 404 
Systemic circulation, 59 
Systemic heart, 104, 195 
Systole, 134 

Tactile, organs, 300 
Tadpole, dissection of, 41 
Taenia, 181 
Tailed birds, 355 
Tapeworms, 181 
Tapirs, 383 
Tarsals, 297 
Tarso-metatarsus, 49 
Tarsus, 38 
Tarsus of insects, 78 
Taste-organs, 301 
Tautog, 332 



436 



INDEX. 



Teeth of mammals, 367 

Teleost, dissection of, 22 

Teleostei, 326 

Telson, 68 

Terebratulina, 190 

Teredo, 207 

Termites, 247 

Tertiary, 414 

Tertiary feathers, 49 

Test, 115 

Testis, 315 

Testudinata, 348 

Tetrabranchiata, 211 

Tetradecapoda, 229 

Thalamencephalon, 299 

Theca, 167 

Thoracic duct, 55 

Thorax of arthropods, 216, 237 

Thrushes, 363 

Thylacine, 371 

Thylacoleo, 372 

Thymus gland, 58, 310 

Thyroid gland, 310 

Thysanura, 243 

Tibia, 45, 78, 297 

Tibio-fibula, 38 

Ticks, 234 

Tiger, 388 

Tiger-beetles, 251 

Tissues, 156 

Toads, 341 

Tongue of butterflies, 263 

Tongue of vertebrates, 305 

Toothed birds, 356 

Tooth, dermal, 17 

Tooth shells, 201 

Torpedo, 324 

Tortoises, 348 

Toucans, 360 

Trachea, 60, 309 

Trachea of arthropods, 80, 217, 

239 
Transverse process, 37, 291 
Tree-hoppers, 260 
Tree-toads, 341 
Trematodes, 180 
Triassic period, 414 
Trichechus, 381 
Trichina, 182 



Trichinosis, 183 
Trigeminal nerve, 20, 300 
Trilobites, 225 
Trochanter, 77 
Trochlearis nerve, 300 
Trochophore, 186, 197 
Tropic bird, 358 
Trout, 328 

Truncus arteriosus, 18 
Trunk-fish, 333 
Trunk-region, 292 
Tube-feet, 110 
Tubicola, 185 
Tunicata, 287 
Tunny, 331 
Turbellaria, 180 
Turbot, 330 
Turkeys, 357 < 
Turtle, dissection of, 44 
Turtles, 348 

'Twixt-brain, 20, 24, 299 
Tympanic membrane, 33, 303 
Tympanic membrane of grass- 
hopper, 76 

Ulna, 45, 297 
Umbo, 98 

Uncinate process, 353 
Ungulata, 383 
Unio, 98, 206 
Ureter, 34, 56 
Urinary bladder, 34, 54 
Urodela, 310 
Urostyle, 37 

Vagus nerve, 21, 59, 300 
Valves of shell, 98, 194 
Vampyre, 378 
Variation, 416 
Velum, 127, 166 
Venous sinus, 26 
Ventral aorta, 18, 26, 310 
Ventral fins, 16, 23 
Ventricle, 18, 26, 59, 310 
Ventricles of brain, 29, 62, 298 
Venus, 203 
Vermes, 178 
Vertebra, 27, 37, 290 
Vertebral column, 27 



INDEX. 



437 



Vertebrata, 290 
Villi, 307 
Vinegar-eels, 182 
Visceral ganglion, 196 
Visceral skeleton, 290, 293 
Vital force, 139 
Vitreous humor, 304 
Vocal chords, 61 
Vomer, 39 
Vorticella, 151 
Vultures, 360 

Walking-stick, 245 
Walrus, 390 
Wasp, study of, 87 
Wasps, 255 
Water-beetles, 251 
Water-skaters, 258 
Water-snakes, 348 
Water vascular system, 117 
Weasels, 388 



Weevils, 250 

Whalebone, 380 

Whales, 378 

White ants, 247 

Whitefish, 328 

White Mountain butterfly, 267 

Wickersheimer's fluid, 6 

Windpipe, 309 

Wing coverts, 49 

Wireworms, 252 

Wishbone, 51, 297, 354 

Wolffian bodies, 18 

Wolves, 388 

Wombat, 371 

Woodchuck, 376 

Woodpeckers, 361 

Worms, 178 

Wrens, 363 

Xiphisternum, 37 

Zooid, 123, 164 



